Black nightshade, large black nightshade, American black nightshade, and glossy black nightshade all belong to the Solanaceae family and Solanum genus. They are very common in urban areas and can even be found in green spaces in large cities. They are characterized by their round, black ripening fruits, but the four species are very similar and sometimes difficult to distinguish. Various identification methods have been proposed, but I think focusing on the characteristics of the flowers and fruits is the simplest. Sometimes, you may just have to accept that there are individuals that are indistinguishable. This article will explain the classification and morphology of the Solanum genus, which produces round, black fruits.

What are black nightshade, large black nightshade, American black nightshade, and glossy black nightshade?

Solanum nigrum, also known as black nightshade or dog nightshade, is an annual plant widely distributed in Hokkaido, Honshu, Shikoku, Kyushu, and the Ryukyu Islands in Japan; Eurasia; and naturalized in the Americas (Kanagawa Prefecture Flora Survey Association, 2018; RBG Kew, 2025). In Japan, it grows along roadsides, cultivated fields, wastelands, and riverbanks.

Solanum nigrescens, also known as large black nightshade, is an annual or perennial plant native to the southern United States, Central America, and northern South America, and has naturalized throughout the world. In Japan, it grows not only in urban areas south of Honshu, but also in riverbeds, cultivated fields, and forest edges in areas slightly closer to mountains.

American nightshade (Solanum emulans) is an annual plant native to Canada and the eastern United States, and has naturalized in Europe and Japan. It grows in harbors and fields throughout Japan. Older literature, such as the "Flora of Kanagawa Prefecture 2018," identifies it as Solanum ptychanthum, but this is now considered a synonym (old scientific name) (Knapp et al., 2019).

Solanum americanum, also known as glossy-fruited black nightshade, is an annual or perennial plant native to Canada and South America that has naturalized worldwide. In Japan, it grows around farmland, riverbanks, coastlines, and forest edges at the foot of mountains.

All of these plants belong to the Solanum genus of the nightshade family, and they are very common in urban areas, and can even be found in green spaces in large cities.

It possesses the characteristic "porous anthers" of the Solanum genus, with large, conspicuous yellow anthers that taper towards the tip and have small holes.

In addition, these four species are characterized by polymorphic leaves, small flowers, and nearly spherical fruits that ripen to purple to black.

The four species mentioned above are very similar and difficult to distinguish. It would be almost impossible to identify them at a glance while walking in the wild.

Furthermore, the existence of various intermediate forms makes accurate identification difficult.

What are the differences between *Solanum nigrum*, *Solanum sibiricum*, *Solanum nigrum*, and *Solanum nigrum*?

Various methods for identifying these four species have been suggested in numerous field guides and websites.

However, the sheer number of points of focus can actually make identification more difficult.

Therefore, I will focus on explaining only the truly important points here (Kanagawa Prefecture Flora Survey Association, 2018).

First, there is a difference in that the corolla of the black nightshade (Solanum nigrum) is shallowly incised, while that of the large black nightshade (Solanum nigrum), American black nightshade (Solanum sempervirens), and glossy black nightshade (Solanum nigrum var. sempervirens), the corolla is deeply incised, extending almost to the base.

Regarding the remaining three species, the fruits of *Solanum nigrum* and *Solanum americanum* are 7-10 mm in diameter, black with a somewhat dull sheen, and the flesh remains green until fully ripe. In contrast, *Solanum sempervirens* has fruits that are 4-7 mm in diameter, ripen to a dark purple color with a strong sheen, and the flesh turns purple earlier.

Regarding the remaining two species, there is a difference in that *Solanum nigrum* has 5 to 8 flowers per inflorescence and the corolla is large, with a diameter of 8 to 12 mm, while *Solanum americanum* has 1 to 4 flowers per inflorescence and the corolla is 4 to 6 mm in diameter.

I think the basic approach is to simply observe the above points. While field guides often mention examining the number of spherical granules and seeds within the fruit, this is not practical for the average person to observe in the field, so I will omit it here. For more detailed information, please refer to the Kanagawa Prefectural Flora Survey Association (2018) or Knapp et al. (2019).

However, there are intermediate individuals, and it can be difficult to distinguish between *Solanum nigrum* and *Solanum americanum* in particular. The notches in the corolla that identify *Solanum nigrum* can also be difficult to discern from certain angles, as the corolla is small and requires careful examination of multiple specimens.

Flower color and the curvature of the corolla lobes are individual variations and should not be used as a reference.

Are there any other similar species?

The Solanum genus includes several species with "black nightshade" in their name, such as Solanum sarrachoides, Solanum physalifolium var. nitidibaccatum, Solanum villosum subsp. villosum, and Solanum villosum subsp. miniatum.

However, in *Solanum nigrum* and *Solanum humile*, the calyx enlarges after flowering, covering half or more of the fruit, so their appearance is quite different.

The fruits of both the velvet nightshade and the red nightshade are elongated ellipsoids and ripen to yellow to red, so there's no chance of confusion.

Other species in the Solanum genus are larger, have different fruit shapes, or are thorny, so they are unlikely to be confused. Please see the separate article for more details. In the case of the Chinese lantern plant, the fruit is enclosed by a persistent calyx.

What are the differences between ground cherries, edible ground cherries (strawberry tomatoes), and tomatoes? We'll explain how to distinguish between similar varieties! Are three types of "edible ground cherries" being confused?

Ground cherries, edible ground cherries (strawberry tomatoes), and tomatoes all belong to the nightshade family and are characterized by producing red fruits. Edible ground cherries are sold under names such as "edible ground cherry" and "strawberry tomato," and there is some confusion about their relationship to ground cherries and tomatoes...

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What are the differences between eggplant and nightshade? What is the origin and evolution of eggplant? Why is nightshade disliked? Does its flower pollinate by vibration? Why are nightshade fruits poisonous?

Both eggplant (Nasu) and nightshade (Nightshade japonica) share the name "eggplant" and have similar flower shapes, so those unfamiliar with them might confuse them. However, eggplant and nightshade are completely different species. Eggplant is a cultivated plant that does not grow wild and has no thorns, while nightshade is a wild plant...

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What are the differences between Solanum lyratum, Solanum sarmentosum, Solanum sarmentosum, and Solanum jasminoides? We'll explain how to distinguish between similar species! What are the structures of their flowers and fruits?

Solanum lyratum, Solanum sarmentosum, Solanum japonica, and Solanum jasminoides all belong to the Solanaceae family and are four species that share the characteristic of being "climbing plants." Their basic flower and fruit structures are the same, which is why they are often confused. However, these four species have clear differences...

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What are the differences between *Tama coral* (winter coral) and *Himeta coral*? An explanation of how to distinguish between similar species.

Both Solanum sieboldii (winter coral) and Solanum nigrum belong to the Solanaceae family and are cultivated extensively for ornamental purposes because they produce attractive, round, red, ripe fruits (berries) in winter. However, in Japan, it is not always possible to properly distinguish between the two varieties, Solanum sieboldii and Solanum nigrum...

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References

Kanagawa Prefecture Flora Survey Association. 2018. Kanagawa Prefecture Flora 2018 (Electronic Edition). Kanagawa Prefecture Flora Survey Association, Odawara. 1803pp. ISBN: 9784991053726

Knapp, S., Barboza, GE, Bohs, L., & Särkinen, T. 2019. A revision of the Morelloid clade of Solanum L. (Solanaceae) in North and Central America and the Caribbean. PhytoKeys 123: 1-144. https://doi.org/10.3897/phytokeys.123.31738

RBG Kew. 2025. The International Plant Names Index and World Checklist of Vascular Plants. Plants of the World Online. http://www.ipni.org and https://powo.science.kew.org/

Physalis, edible physalis (strawberry tomato), and tomatoes all belong to the Solanaceae family and are characterized by producing red fruits. Edible physalis is sold under the names "edible physalis" and "strawberry tomato," and is often introduced as if it is related to physalis or tomatoes, but it is a completely different species. In fact, their distribution areas and classifications are different, and there are various differences in their morphology. It should also be noted that "edible physalis" refers not only to edible physalis but also to other species such as grape physalis (golden berry) and large grape physalis (tomatillo), and is often confused with them. This article will explain the classification and morphology of physalis species.

What are Chinese lantern plants, edible lantern plants, and tomatoes?

Alkekengi officinarum var. franchetii, also known as Chinese lantern plant (Physalis alkekengi var. franchetii), is a perennial plant distributed from central China to the Korean Peninsula and introduced to surrounding countries, including Japan, for ornamental purposes (RBG Kew, 2025). In Japan, cultivated plants sometimes escape cultivation. While the "Flora of Kanagawa Prefecture 2018" and many websites list its scientific name as Physalis alkekengi var. franchetii, this is now considered a synonym (old scientific name) (Whitson, 2011).

Physalis grisea, also known as strawberry tomato, cherry tomato, orange cherry, summer cherry, kasennari, or sticky ground cherry, is a perennial plant distributed in the eastern United States and introduced to North America and Europe for food. It is sometimes listed on websites under the scientific name Physalis pruinosa, but this is a synonym (old scientific name). It is also sometimes described as being native to Europe, but this is false.

The tomato , Solanum lycopersicum, is also known as red eggplant. It is a perennial plant (though it is treated as an annual in Japan because it cannot survive the winter) that is distributed in Peru (the Andes Mountains plateau) and cultivated for food all over the world.

All of these plants belong to the nightshade family and are characterized by producing red fruits.

The edible ground cherry (Physalis alkekengi) is sold under names such as "edible ground cherry" or "strawberry tomato," giving the impression that it is related to ground cherries and tomatoes. In fact, the shape of its leaves is similar to that of ground cherries, and the shape of its fruit is similar to that of tomatoes.

Therefore, some people may mistakenly believe that edible ground cherry (Physalis alkekengi) is a cultivated variety of the Chinese lantern plant (Physalis alkekengi), or that edible ground cherry (Physalis alkekengi) is a cultivated variety of the cherry tomato (Solanum lycopersicum var. cerasiforme).

When reading articles on the internet, it's common to see descriptions that make it seem as if the difference is simply a matter of variety.

What are the differences between ground cherry, edible ground cherry, and tomato?

However, this is completely wrong, and their distribution in the wild is fundamentally different (Kanagawa Prefecture Flora Survey Association, 2018; Flora of North America Editorial Committee, 2023).

As mentioned above, the ground cherry (Physalis alkekengi) is distributed in East Asia, the edible ground cherry (Physalis edulis) in North America, and the tomato in South America. It's unlikely they are the same species.

Furthermore, although there are various theories regarding classification, the Chinese lantern plant (Physalis) belongs to the Physalis genus, the edible lantern plant (Physalis genus) belongs to the Physalis genus, and the tomato belongs to the Solanum genus, which is another point of difference.

Morphologically, there are the following differences:

Regarding the leaves, there are differences: Chinese lantern plants have simple leaves with almost no wrinkles on the upper surface, edible lantern plants have simple leaves with many wrinkles on the upper surface, and tomatoes have odd-pinnately compound leaves.

Regarding the flowers, the difference lies in the fact that the Chinese lantern plant and edible lantern plant have coffee bean-shaped anthers on their stamens that split vertically to release pollen, while the tomato plant has large, banana-shaped, yellow anthers on its stamens that open at the top to release pollen. The tomato plant's unique anthers are called "porous anthers" and have evolved specifically for bees such as bumblebees that generate vibrations.

Comparing the Chinese lantern plant (Physalis alkekengi) and the edible Chinese lantern plant (Physalis chinensis), the difference is that the corolla of the Chinese lantern plant is basically white with a green center, while the corolla of the edible Chinese lantern plant is basically cream-colored with a black center.

You might be most interested in the difference in the fruit, but in Chinese lantern plants and edible lantern plants, the calyx that was on the flower completely encloses the fruit, which is called a "persistent calyx," whereas in tomatoes this does not happen, and the green calyx remains on top of the fruit.

Comparing the Chinese lantern plant (Physalis alkekengi) and the edible lantern plant (Physalis edulis), the Chinese lantern plant has a persistent calyx that turns red when ripe, and the fruit itself is also red and large, while the edible lantern plant has a persistent calyx that turns yellow when ripe, and the fruit itself is yellow and small. Furthermore, the persistent calyx of the Chinese lantern plant is hairless, while that of the edible lantern plant is hairy.

Incidentally, small tomatoes are called "mame tomato" (bean tomato) Solanum lycopersicum var. cerasiforme, and are also known as mameakanasu or himetomatoma, but the product name "mini tomato," given by Takii Seed Co., Ltd. to its small tomato varieties, has become firmly established.

Hearing this, one might mistakenly think that the large-fruited tomato, Solanum lycopersicum var. lycopersicum, is the original form (the wild species), but in reality, the smaller-fruited variety, like the cherry tomato, is the wild species, and tomatoes have grown larger as a result of selective breeding. If you think about it, if tomatoes that big were to grow in the wild, they would be eaten in abundance.

What are the differences in taste between ground cherries, edible ground cherries, and tomatoes?

Many people might be concerned about the taste.

Ground cherries are poisonous and bitter, containing a lot of solanine, and are not edible.

Fujimi Sky Farm describes the edible ground cherry as follows: "At first glance, it resembles an orange cherry tomato, but the first thing that surprises you when you take a bite is its rich flavor. The noble aroma reminiscent of mango or lychee, the juicy and fruity sweetness like melon or grape, and the fresh acidity combine to give you a new kind of deliciousness you've never tasted before."

As many people know, tomatoes have a sweet and sour taste.

Are there any other similar varieties? It seems that three different types of "edible ground cherries" are being confused!

When referred to as "edible ground cherry," it is often confused with the grape ground cherry (Physalis peruviana). However, the edible ground cherry is native to the United States, grows creeping and spreading, and its fruit has a complex, sweet flavor like pineapple or melon, while the grape ground cherry is native to northern South America, grows very large and upright, and its fruit has a citrusy flavor (Ristvey, 2025). The leaves of the grape ground cherry are less wrinkled. Other names for the grape ground cherry include striped ground cherry, hairy ground cherry, golden berry, and Inca berry. It is sometimes said that the grape ground cherry is native to Europe, but this is false.

When searching for edible ground cherries, you might come across the name "tomatillo," but this is a completely different species from the edible ground cherry (Physalis philadelphica). Tomatillos have yellow flowers, and their persistent calyxes are attached to large fruits. They are used in Latin American cuisine.

Physalis angulata, also known as edible ground cherry, is similar to the edible ground cherry, but its persistent calyx remains green even when mature. The center of the flower may be colorless or purple, but it never turns black. It is not edible.

References

Flora of North America Editorial Committee. (2023). Flora of North America (Vol. 14 Magnoliophyta: Gentianaceae to Hydroleaceae). Oxford University Press. ISBN: 9780197691465

Kanagawa Prefecture Flora Survey Association. (2018). Kanagawa Prefecture Flora 2018 Electronic Edition. Kanagawa Prefecture Flora Survey Association. ISBN: 9784991053726

RBG Kew. (2025). The International Plant Names Index and World Checklist of Vascular Plants. Plants of the World Online. http://www.ipni.org and https://powo.science.kew.org/

Ristvey, A. (2025, April 26). Goldenberry. University of Maryland Extension. https://extension.umd.edu/programs/agriculture-food-systems/program-areas/fruit-vegetable-production/alternative-crops/goldenberry/

Whitson, M. (2011). (2016) Proposal to conserve the name Physalis (Solanaceae) with a conserved type. Taxon, 60 (2), 608-609. https://doi.org/10.1002/tax.602047

Both Solanum sieboldii (winter coral) and Solanum nigrum belong to the Solanaceae family and are cultivated extensively for ornamental purposes because they produce attractive, round, red, ripe fruits (berries) in winter. However, few people in Japan can properly distinguish between the two varieties. The two varieties can be easily distinguished by checking the amount of hair covering their entire body. This article will explain the classification and morphology of the Solanum genus, which consists of evergreen shrubs.

What are *Tama coral* and *Himeta tama coral*?

Solanum pseudocapsicum var. pseudocapsicum, also known as winter coral, is native to South America (Brazil, Argentina, Chile, Uruguay, and Paraguay) and is cultivated as an ornamental plant worldwide, including in Japan. It was introduced to Japan in the mid-Meiji era and is cultivated for ornamental purposes, but it has also naturalized along roadsides in warmer regions.

Solanum pseudocapsicum var. diflorum, also known as Himetama coral (princess ball coral), is an evergreen shrub of unknown origin (possibly the same as ball coral?) that is cultivated for ornamental purposes all over the world, including Japan.

All of these plants belong to the Solanum genus of the nightshade family, and they are widely cultivated for ornamental purposes because they produce round, red, ripe fruits (berries) in winter, making them visually appealing.

Morphologically, a distinctive feature of this species within the Solanum genus is its erect stem and evergreen shrub-like structure, which is helpful for identification (Kanagawa Prefecture Flora Survey Association, 2018).

However, it seems that few people in Japan properly distinguish between the two varieties, *Tama-sango* and *Hime-tama-sango*. While they are described in 'Ylist', the most comprehensive list of correspondences between Japanese and scientific names, there are few websites that appear when you search for *Hime-tama-sango* on Google, and some field guides do not include both varieties.

On the other hand, two varieties are distinguished in Chinese botanical guides (Wu & Raven, 1994).

What is the difference between *Tama coral* and *Himeta coral*?

Distinguishing between *Tinea japonica* and *Tinea japonica* is quite easy (Wu & Raven, 1994).

In *Tama-sango*, the entire body is hairless and the anthers of the flower stamens are 2 mm or longer, whereas in *Hime-tama-sango*, the entire body is hairy and the anthers of the flower stamens are about 2 mm long.

The hair all over this animal is so thick that it's clearly visible even from a distance, so if you know what it is, you won't mistake it for anything else.

The book "Ylist" suggests that "most of the tama corals in Japan are actually dwarf tama corals," but I have confirmed the presence of both in Japan. However, it's possible that one of them is rare, and this may become clearer as more people learn to distinguish between them properly in the future.

It should be noted that some research institutions in the UK do not distinguish between the two varieties, and some do not consider them to be separate varieties (RBG Kew, 2024).

Are there any other similar species?

As mentioned above, winter coral belongs to the Solanum genus, which contains a vast number of species, but it can be easily identified by its evergreen shrub and upright stem.

For information on other members of the Solanum genus, please see our other articles.

What are the differences between eggplant and nightshade? What is the origin and evolution of eggplant? Why is nightshade disliked? Does its flower pollinate by vibration? Why are nightshade fruits poisonous?

Both eggplant (Nasu) and nightshade (Nightshade japonica) share the name "eggplant" and have similar flower shapes, so those unfamiliar with them might confuse them. However, eggplant and nightshade are completely different species. Eggplant is a cultivated plant that does not grow wild and has no thorns, while nightshade is a wild plant...

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What are the differences between Solanum lyratum, Solanum sarmentosum, Solanum sarmentosum, and Solanum jasminoides? We'll explain how to distinguish between similar species! What are the structures of their flowers and fruits?

Solanum lyratum, Solanum sarmentosum, Solanum japonica, and Solanum jasminoides all belong to the Solanaceae family and are four species that share the characteristic of being "climbing plants." Their basic flower and fruit structures are the same, which is why they are often confused. However, these four species have clear differences...

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What are the differences between *Solanum nigrum*, *Solanum sibiricum*, *Solanum nigrum*, and *Solanum nigrum*? We'll explain how to distinguish between similar species!

Black nightshade, large black nightshade, American black nightshade, and glossy black nightshade all belong to the Solanaceae family and Solanum genus. They are very commonly seen in urban areas, and can even be found in green spaces in large cities. They are characterized by their round, black, ripening fruits, but the four species are very similar...

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References

Kanagawa Prefecture Flora Survey Association. 2018. Kanagawa Prefecture Flora 2018 (Electronic Edition). Kanagawa Prefecture Flora Survey Association, Odawara. 1803pp. ISBN: 9784991053726

RBG Kew. 2024. The International Plant Names Index and World Checklist of Vascular Plants. Plants of the World Online. http://www.ipni.org and https://powo.science.kew.org/

Wu, ZY, & Raven, PH (Eds.). 1994. Flora of China (Vol. 17 Verbenaceae through Solanaceae). Science Press, Beijing, and Missouri Botanical Garden Press, St. Louis. 342pp. ISBN: 9780915279241

Datura stramonium, Datura stramonium, and Datura arborescens all belong to the Solanaceae family and are cultivated as ornamental plants, as well as being well-known as poisonous and medicinal plants. They are also collectively called "Datura" or "Datura" from their genus name. However, these species are often confused and misunderstood on the internet. First, there is a major classification difference: Datura stramonium and Datura stramonium belong to the Datura genus, while Datura arborescens belongs to the Datura genus. Specifically, there are differences in flower size and the direction in which they bloom. Datura stramonium and Datura stramonium can be roughly distinguished by the presence or absence of hairs, but it is rare to see genuine Datura stramonium in Japan in the first place. There are also many other species in the same genus, so be sure to distinguish them as well. This article will explain the classification of the Datura genus and the Datura genus.

What are Datura stramonium, Datura stramonium, and Datura arborescens?

Datura metel, also known as Korean morning glory, is native to Central and South America and is an annual plant that grows on sunny, grassy slopes (Kanagawa Prefecture Flora Survey Association, 2018; RBG Kew, 2023). It was introduced to Asia a long time ago and has naturalized in Africa and other regions. In Japan, it was introduced during the Edo period and cultivated for medicinal purposes, but it is now rarely seen.

Datura wrightii, also known as hairy morning glory, is a perennial plant native to the United States and Mexico, growing in vacant lots and other open spaces. It is cultivated in various parts of the world and sometimes becomes naturalized. It was introduced to Japan at the end of the Edo period, cultivated for ornamental purposes, and sometimes becomes naturalized.

Brugmansia suaveolens, also known as angel's trumpet, is an evergreen shrub native to Brazil. It is cultivated and sometimes naturalized in various parts of the world, including Japan.

All of these plants belong to the Solanaceae family and are cultivated as ornamental plants. They are also well-known as poisonous and medicinal plants containing tropane alkaloids such as atropine, scopolamine, and hyoscyamine. They are collectively referred to as "Datura" or "Datura" from their genus name (however, Datura arborescens is no longer included in the Datura genus).

Other common features include flowers that are 5 cm or longer and grow solitary, and fruits that are capsules. These are characteristics that are rare within the Solanaceae family. The fact that the tip of the corolla extends into a tail-like shape is a major difference from sympetalous flowers such as morning glories.

However, these varieties are extremely often confused. In particular, there is almost no mention of the difference between Datura stramonium and Datura metel on the internet, and what should be Datura metel is often mistakenly identified as Datura stramonium.

What are the differences between the Datura genus and the Datura genus?

These species are completely different (Editorial Committee of the Flora of Taiwan, 1998; Spencer, 2002).

First, there is a major difference between Datura stramonium and Datura metel, which belong to the genus Datura, while Brugmansia stramonium belongs to the genus Brugmansia. Brugmansia stramonium was once classified under the genus Datura, but this is its current classification.

Therefore, it can be expected that there will be significant differences in their characteristics.

Specifically, while the genus Datura consists of herbs to subshrubs, the genus Datura consists of evergreen shrubs to trees, clearly indicating a larger size. This is as the name "tree" suggests.

Furthermore, while the flowers of the Datura genus are small, less than 20 cm in diameter, and tend to grow somewhat upright, the flowers of the Datura genus are large, more than 20 cm in diameter, and tend to droop downwards.

These two points are arguably the biggest differences. There are other minor differences, but I will omit them here.

Therefore, these characteristics allow us to distinguish the tree dwarf stramonium from the common stramonium and the hairy stramonium.

While *Datura stramonium* is the most common species of the *Datura* genus found in Japan, several other species, such as * Brugmansia x candida*, are also cultivated and have Japanese names. For information on how to distinguish between them, please refer to Spencer (2002).

What is the difference between Datura stramonium and Datura metel?

There are probably very few resources that describe the differences between Datura stramonium and Datura metel.

You might think that the Korean stramonium (Datura stramonium) is a well-known name and can be seen in your local area.

However, while true Datura stramonium was once cultivated as mentioned above, it is now rarely seen, and what is commonly seen today is Datura stramonium (Kanagawa Prefecture Flora Survey Association, 2018).

The main difference is that in Datura stramonium, the stems and leaves are almost hairless except for the young parts, and the capsules are erect or obliquely ascending, whereas in Datura stramonium, the stems and leaves are densely covered with fine, soft hairs, and the capsules face downwards.

As you can see, the Datura stramonium has hairs, which gives its stem a whitish appearance, making it easy to spot.

However, other species of the Datura genus found in Japan are also known.

White-flowered Datura stramonium var. stramonium has stems and leaves that are almost hairless, and its fruit has spines less than 1 cm long. It is as common as, or even more common than, the common Datura stramonium. Although its name means "white flower," there is also f. stramonium with pale green stems and white flowers, and there is also f. tatura, which has purplish stems and pale purple flowers.

Datura stramonium var. inermis has stems and leaves that are almost hairless, and its fruits have no thorns.

Datura ferox has stems and leaves that are almost hairless, and its fruit has thick spines 1-2 cm long.

References

Editorial Committee of the Flora of Taiwan. 1998. Flora of Taiwan (2nd ed., Vol. 4). Taiwan University, Taipei. 1217pp. ISBN: 9789570231212, http://www.efloras.org/florataxon.aspx?flora_id=100&taxon_id=10828

Kanagawa Prefecture Flora Survey Association. 2018. Kanagawa Prefecture Flora 2018 (Electronic Edition). Kanagawa Prefecture Flora Survey Association, Odawara. 1803pp. ISBN: 9784991053726

RBG Kew. 2023. The International Plant Names Index and World Checklist of Vascular Plants. Plants of the World Online. http://www.ipni.org and https://powo.science.kew.org/

Spencer, R. 2002. Solanaceae. In: R. Spencer (Ed.), Horticultural Flora of South-eastern Australia: The identification of garden and cultivated plants (Vol. 4. Flowering plants. Dicotyledons. Part 3). University of New South Wales Press, Sydney. ISBN: 9780868406848, https://hortflora.rbg.vic.gov.au/taxon/812e4f6e-edbc-42bc-b528-63c3ac4e14df/key, https://hortflora.rbg.vic.gov.au/taxon/ad9df2e0-5340-11e7-b82b-005056b0018f/key

Solanum lyratum, Solanum sulphureum, Solanum holosteoides, and Solanum jasminoides all belong to the Solanaceae family and are four species that share the characteristic of being "climbing plants." The basic structure of their flowers and fruits is the same, so these four species are often confused. However, these four species have clear differences. Solanum jasminoides and Solanum sulphureum are completely different species. This can be determined by examining the hairs on the stem and the shape of the leaves. The flowers are sympetalous and have yellow, perforated anthers like a banana. The fruit is a berry. This article will explain the classification and morphology of climbing Solanum species.

What are Japanese honeysuckle, mountain dappled, round-leaved dappled, and crescent-leaf nightshade?

Solanum lyratum, also known as Japanese honeysuckle, is a climbing perennial herb that grows at the edges of forests and is distributed in Hokkaido, Honshu, Shikoku, Kyushu, and the Ryukyu Islands in Japan; as well as in Korea, China, and Southeast Asia (Kanagawa Prefecture Flora Survey Association, 2018).

Solanum japonense, also known as Yamahoroshi, is a climbing perennial herb distributed in Hokkaido, Honshu, Shikoku, and Kyushu in Japan; as well as in Korea and China, growing in forest edges and within forests (Kadota et al., 2013).

Solanum maximowiczii, also known as round-leaved holly, is a climbing perennial herb distributed in Honshu (west of the southern Kanto region), Shikoku, Kyushu, and the Ryukyu Islands of Japan, growing in evergreen broad-leaved forests and valleys at the foot of mountains (Ohashi et al., 2017).

Solanum laxum, also known as climbing nightshade, is a perennial vine distributed in southeastern Brazil, Argentina, and the La Plata River estuary in Uruguay, growing in Atlantic coastal forests, Norfolk Island forests, riparian forests, and open forest edges (Brazil Flora G., 2023). It is widely cultivated as an ornamental plant in both temperate and subtropical regions worldwide, including Japan, and has naturalized and become naturalized in places like Australia and New Zealand.

All four species belong to the Solanaceae family, specifically the Solanum genus, and are characterized by their "climbing" growth habit. Their basic flower and fruit structures are the same.

Regarding *Solanum lyratum*, *Solanum lyratum*, and *Solanum sarmentosum*, they can be said to belong to a similar group of wild species. They also share the characteristic of having corollas that sometimes curve backward.

Furthermore, the plant Solanum jasminoides is sometimes called "Yamahoroshi" in horticulture as an alternative name, making the two species easily confused. Distinguishing them based solely on their leaves seems difficult.

What are the differences between Solanum lyratum, Solanum sulphureum, Solanum holosteoides, and Solanum jasminoides?

However, these four species have clear differences. Solanum jasminoides and Solanum sarmentosum are also completely different species.

First, since Solanum lyratum, Solanum sulphureum, and Solanum holosteoides are wild species, and Solanum jasminoides is a cultivated species, it's safe to assume that Solanum jasminoides is not commonly found in the wild in Japan.

We will also consider morphological differences.

Firstly, in Solanum lyratum, the stem is densely covered with glandular hairs of varying lengths, whereas in Solanum sarmentosum, Solanum holosteoides, and Solanum jasminoides, the stem is either hairless or has only a few soft hairs.

Regarding the remaining three species, the differences are as follows: in Solanum sarmentosum and Solanum holosteoides, the corolla is deeply incised, the lobes sometimes curve backward, and the color is purple with a yellowish-green inner throat; in Solanum jasminoides, the corolla is shallowly incised, the lobes do not curve backward, and the color is entirely white to pale purple.

Distinguishing between Solanum sarmentosum and Solanum holosteoides is the most difficult, but in Solanum sarmentosum, the leaves are ovate or ovate-lanceolate, with a heart-shaped, rounded, or truncate base, and entire, wavy, or serrated margins, sometimes 3-5 lobed near the base, while in Solanum holosteoides, the leaves are elliptical or ovate-lanceolate, with a wedge-shaped base that flows into the petiole, and are entire and undivided.

There are many distinguishing features, but the shape of the base of the leaf blade is probably the easiest to identify. The Japanese name "Marubanohoroshi" (round-leaved holly) certainly describes a characteristic feature, but it's important to note that even Yamahoroshi can have entire, undivided margins.

Other differences include the fact that in Solanum sarmentosum, the upper surface of young leaves has distinct hairs and the inner surface of the flower throat is dark purple, while in Solanum sarmentosum, the upper surface of young leaves has scattered dot-like projections and the inner surface of the flower throat is green.

Are there any other similar species?

The Solanum genus includes many other species, but the number of climbing herbaceous plants is limited.

For those who want to know the difference between Solanum species with upright stems and those with woody stems, please see our other article.

What are the differences between eggplant and nightshade? What is the origin and evolution of eggplant? Why is nightshade disliked? Does its flower pollinate by vibration? Why are nightshade fruits poisonous?

Both eggplant (Nasu) and nightshade (Nightshade japonica) share the name "eggplant" and have similar flower shapes, so those unfamiliar with them might confuse them. However, eggplant and nightshade are completely different species. Eggplant is a cultivated plant that does not grow wild and has no thorns, while nightshade is a wild plant...

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What are the differences between *Tama coral* (winter coral) and *Himeta coral*? An explanation of how to distinguish between similar species.

Both Solanum sieboldii (winter coral) and Solanum nigrum belong to the Solanaceae family and are cultivated extensively for ornamental purposes because they produce attractive, round, red, ripe fruits (berries) in winter. However, in Japan, it is not always possible to properly distinguish between the two varieties, Solanum sieboldii and Solanum nigrum...

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What are the differences between *Solanum nigrum*, *Solanum sibiricum*, *Solanum nigrum*, and *Solanum nigrum*? We'll explain how to distinguish between similar species!

Black nightshade, large black nightshade, American black nightshade, and glossy black nightshade all belong to the Solanaceae family and Solanum genus. They are very commonly seen in urban areas, and can even be found in green spaces in large cities. They are characterized by their round, black, ripening fruits, but the four species are very similar...

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What is the structure of a flower?

Flowers of the Solanum genus are all fused-petal flowers, and this is true for all four species. In particular, the stamens have a distinctive feature common to all species in the Solanum genus.

This is because the anthers, which are the pollen-containing parts of the stamen, are large and conspicuous, and these anthers taper to a point with a small hole. Such anthers are called "porous anthers" (Shimizu, 2001).

Japanese honeysuckle (Solanum lyratum) blooms from August to September. Numerous flowers are borne in cymose inflorescences. The corolla is white, about 1 cm in diameter, deeply divided into five lobes, with the lobes curving backward. There are five stamens, with thick, short filaments. The anthers are yellow.

Solanum sarmentosum flowers from July to September. It bears sparsely branched cymose inflorescences with several flowers, originating from the opposite side of the leaves or partway up the stem. The calyx is saucer-shaped and has five lobes at the tip. The pedicels thicken slightly below the calyx. The corolla is pale purple, deeply five-lobed, and about 1 cm in diameter. Initially, it spreads flat, but later each lobe curves strongly backward. There are yellowish-green glands at the base of the lobes, and the inner surface of the throat is dark purple. There are five yellow stamens, clustered in the center of the flower and erect. The anthers are oblong, about 3 mm long, and surround the pistil.

Solanum sieboldii flowers from August to September. It produces sparsely branched cymose inflorescences from the middle of the stem or from the opposite side of the leaves. The calyx is saucer-shaped and shallowly 5-lobed. The corolla is pale purple, deeply 5-lobed at the tip, about 1 cm in diameter, with a yellowish-green inner surface of the throat, and the lobes strongly curve backward when open. The anthers are oblong, not tapering at the tip, and about 3 mm long.

Solanum jasminoides flowers from June to October. The inflorescence is terminal or laterally attached, over 5 cm long, and branches many times, although usually only 2-3 times, bearing up to 50 flowers, and is hairless. The calyx is 1-1.5 mm, conical to slightly flattened. The corolla is 1.8-2.2 cm in diameter, white or pale purple, star-shaped, and split about halfway down to the base, with lobes 7-9 x 5-6 mm, spreading out flat when in bloom. The anthers are 3.5-4 mm long and oval-shaped.

What is the structure of the fruit?

These four species, like other members of the Solanum genus, have berries.

The berries of the Japanese honeysuckle are spherical, about 8 mm in diameter, and ripen to a reddish color.

The berries of Solanum sarmentosum are spherical, 6-7 mm in diameter, and occasionally oval-shaped, ripening to red in the autumn. The seeds are approximately 2 mm in diameter.

The berries of Solanum sieboldii are spherical, turning red when ripe, and measuring 7-10 mm in diameter. The seeds are approximately 3 mm in diameter.

The berries of Solanum jasminoides are spherical, about 1 cm in diameter. When ripe, they turn dark purple, and the pericarp is thin and glossy. Each fruit contains 10 to 20 seeds, each about 3 x 2.5 mm, flattened, kidney-shaped, light brown, and has a surface with fine pores.

References

Brazil Flora G. 2023. Brazilian Flora 2020 project. Version 393.387. Instituto de Pesquisas Jardim Botanico do Rio de Janeiro. https://doi.org/10.15468/1mtkaw

Kadota, Y., Nagata, Y., & Azegami, N. 2013. Flowers Blooming in the Mountains (Revised and Expanded New Edition). Yama-kei Publishers, Tokyo. 616pp. ISBN: 9784635070218

Kanagawa Prefecture Flora Survey Association. 2018. Kanagawa Prefecture Flora 2018 (Electronic Edition). Kanagawa Prefecture Flora Survey Association, Odawara. 1803pp. ISBN: 9784991053726

Ohashi, Hiroyoshi; Kadota, Yuichi; Murata, Hitoshi; Yonekura, Koji; and Kihara, Hiroshi. 2017. Wild Plants of Japan (Revised New Edition, Vol. 5: Convolvulaceae to Caprifoliaceae). Heibonsha, Tokyo. 760pp. ISBN: 9784582535358

Shimizu, Takemi. 2001. Illustrated Dictionary of Botanical Terms. Yasaka Shobo, Tokyo. xii, 323pp. ISBN: 9784896944792

Goji berries (Lycium chinense) and Elaeagnus umbellata (Elaeagnus umbellata) share the common characteristic of producing delicious red berries in the summer. However, their botanical characteristics are quite different. The most reliable way to distinguish between goji berries and Elaeagnus umbellata is by their leaves and flowers, although there are also differences in the fruit stalks. Goji berries can be eaten raw, but they are described as having a "fishy smell, a very bland taste, and a slight bitterness," and may not be very tasty unless processed. On the other hand, Elaeagnus umbellata, particularly Elaeagnus macrophylla, is considered delicious. Goji berries are primarily eaten as dried fruit, and the leaves and buds are also edible and used in traditional Chinese medicine. Goji berry flowers, perhaps because they belong to the nightshade family, are conspicuously purple, but their shape is not particularly specialized, resembling a typical flower, and are likely mainly visited by small bees. In nature, the fruit is used by birds and raccoons. This article will explain the classification, uses, pollination ecology, and seed dispersal of goji berries (Lycium chinense) and Elaeagnus multiflora (Elaeagnus multiflora).

A delicious red berry that ripens in the summer.

Goji berry (Lycium chinense) is a shrub distributed throughout Japan, the Korean Peninsula, China, and Taiwan (Hirano, 1997). It is cultivated and sometimes naturalized in South Asia (Nepal), Southeast Asia (Thailand, Malaysia, Indonesia), and Europe (Paisooksantivatana, 1994), and has recently spread to North America (Shirataka, 2018). It inhabits plains with wasteland such as embankments and ditches, and sandy areas near water (Tanaka, 1995; Ohashi et al., 2017). It is cultivated for its edible fruits and leaves.

Botanically, "gumi" (茱萸) is a general term for the genus Elaeagnus and does not refer to a specific plant species. However, in horticulture, it generally refers to Elaeagnus multiflora var. hortensis, or Elaeagnus multiflora var. gigantea, a cultivar of Elaeagnus multiflora with large fruits (Funakoshi, 2017). Elaeagnus multiflora var. gigantea is also called "bikkuri gumi" (surprise gumi) in horticulture.

Elaeagnus multiflora is a deciduous shrub distributed in Hokkaido (Oshima Peninsula) and Honshu (the Sea of Japan side north of central Japan, and central Kinki region), growing in forest edges and within woodlands (Kanagawa Prefecture Flora Survey Association, 2018). It is cultivated for its edible fruit.

From a distance, both goji berries and jujubes appear to be delicious-looking red berries, and their leaves are oblong to oval-shaped, so someone unfamiliar with them might not be able to distinguish them just by looking at the fruit.

The most reliable way to distinguish between goji berries and Elaeagnus umbellata is by their leaves and flowers; the fruits differ in their pedicels.

However, goji berries belong to the nightshade family, while jujubes belong to the Elaeagnaceae family; their classifications are completely different and are the result of convergent evolution. There are considerable differences in their leaves and stems.

First, there is a striking difference in the leaves. The leaves of the goji berry are soft, papery, and hairless, while those of the Chinese olive have silvery-white or brownish scale-like or stellate hairs, and from a distance, countless tiny dots are visible, giving them a sparkling appearance.

Regarding the stems, goji berries (Lycium chinense) have ridges (horns) and thorns. Chinese jack-in-the-valley (Elaeagnus umbellata) has no ridges and no thorns. However, be aware that other species in the Elaeagnus genus may have thorns.

The flowers are completely different; in the wolfberry, the corolla is pale purple and broadly funnel-shaped, whereas in this species, the flower is pale yellow and the calyx tube, which replaces the corolla, is cylindrical.

The most difficult part is the fruit, and first of all, there is a difference in the fruiting period. Goji berries fruit from August to November, while angelica tree berries fruit from June to July. However, depending on the region and weather, there may be some overlap.

Another difference is that the fruit stalk, the elongated organ that attaches the fruit to the plant, is thick and round at the fruit end in goji berries before abruptly narrowing, whereas in angelica trees it remains consistently thin.

Based on the above, you can definitely distinguish them. Judging them by the shape or color of the fruit would be quite difficult.

If you want to learn how to distinguish between different types of gummy candies, please see our other article.

What are the differences between autumn olive, summer olive, Chinese olive, and white olive? Can they be eaten raw? Is the "sparkle" on the leaves to prevent drying? What insects visit the flowers? Are the sweet and sour fruits very popular in nature?

Autumn olive, summer olive, Chinese olive, and white olive are all members of the Elaeagnus genus in the Elaeagnaceae family. They can be found in various locations throughout Japan, including rivers, coastlines, and forests. Their leaves are covered in shimmering stellate or scale-like hairs, and they produce pale yellow flowers consisting only of a cylindrical calyx tube, lacking petals.

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While goji berries can be eaten raw, is eating them raw not so great?

The goji berry is best known for its red berries, and nowadays, it's most familiar to humans as a dried fruit. While it can be eaten fresh, some say it has a "fishy smell, a very bland taste, and a slight bitterness," so it's not very tasty.

In addition, the young shoots in spring and the leaves from summer to autumn are boiled and rinsed in water to be used in salads or blanched dishes, while the raw berries are thoroughly washed and used in tempura, stir-fries, or soups. The fully ripened berries are thoroughly washed and steeped in white liquor to make fruit wine. The leaves and roots are finely chopped and dried to make goji berry tea.

The fruit, root bark, and leaves are also used in traditional Chinese medicine (Shirataka, 2018).

Besides being eaten fresh, the Japanese laurel (Elaeagnus multiflora) is used in jams and other products, as well as to make fruit wine (Elaeagnus multiflora wine). There are various opinions on the taste of eating it fresh, with some saying it is "sweet and sour with a lingering astringency," and others saying it is "almost astringent and sweet enough to be eaten raw." However, the cultivated variety, Elaeagnus macrophylla, is generally considered delicious. Other species of Elaeagnus multiflora, however, are often very sour or bitter and would be difficult to eat without processing.

Are bees primarily attracted to flowers of the nightshade family that have completely different anther shapes?

The flowers of the goji berry are just as vibrant as the fruit, pale purple, and funnel-shaped (Ohashi et al., 2017). They bloom from July to November, from summer to autumn. Although they belong to the same Solanaceae family as eggplants, the shape of their stamens is completely different, with the anthers of the typical form protruding from the outside of the flower.

According to overseas records, this flower is visited by bees, flies, and ants (Paisooksantivatana, 1994), and in Japan, honeybees (Howes, 2015) and red-winged bumblebees (Ikutome, 1992) have also been confirmed. A Google image search also confirmed that a species of bumblebee and a yellow-breasted bumblebee have visited the flower in Japan. There does not seem to be any research yet that has investigated the overall proportion of these species, but it is thought that in Japan, there are many bees that can extend their mouthparts into the funnel-shaped opening.

While pollination in the Solanum genus, including eggplant, is limited to bees capable of vibration pollination, goji berries seem to be able to accommodate a variety of bees. The reason why this method of pollination works is not yet fully understood, but it may be because they have evolved in an environment where there are few insects that steal nectar from outside the flower without carrying pollen, such as bumblebees. However, there are also photographs of bumblebees visiting, so the actual reason remains unclear and research is insufficient.

What are the differences between eggplant and nightshade? What is the origin and evolution of eggplant? Why is nightshade disliked? Does its flower pollinate by vibration? Why are nightshade fruits poisonous?

Both eggplant (Nasu) and nightshade (Nightshade japonica) share the name "eggplant" and have similar flower shapes, so those unfamiliar with them might confuse them. However, eggplant and nightshade are completely different species. Eggplant is a cultivated plant that does not grow wild and has no thorns, while nightshade is a wild plant...

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Do birds and mammals eat goji berries?

What animals in the wild eat goji berries, which can only be enjoyed after being processed by humans?

While this point has not been studied sufficiently, the presence of goji berry seeds carried by birds under persimmon trees suggests that dispersal by birds is a possibility (Takatsuki, 2021).

However, there are also reports that it is being used by raccoons (Takatsuki, 2018).

It's possible that both methods are used, but since it grows in sandy areas near water, bird dispersal might be the primary method. A Chinese study also treats it as bird dispersal (Li et al., 2006).

However, it seems that it is not known which types of birds prefer it.

References

Funakoshi, Ryoji. 2017. 100 Fruit Trees You Can Grow and Eat Yourself: From Familiar Fruits to Popular Berries. Shufunotomo Co., Ltd., Tokyo. 167pp. ISBN: 9784074272013

Hirano, Takahisa. 1997. Tree Guidebook: Understanding the Characteristics and Uses of Trees Found in Gardens, Parks, and Wildlife. Nagaoka Shoten, Tokyo. 319pp. ISBN: 9784522215579

Howes, FN 2015. Plants and Beekeeping. Andesite Press, California. 264pp. ISBN: 9781296522247

Ikutome, Shuichi. 1992. Environment and bee fauna of urban nature parks: Survey results in Shiroyama Park, Kagoshima City. Appendix: Revised Catalogue of bees in mainland Kagoshima Prefecture. Bulletin of Kagoshima Women's Junior College 27: 99-135. ISSN: 0286-8970, http://id.nii.ac.jp/1121/00000877/

Kanagawa Prefecture Flora Survey Association. 2018. Kanagawa Prefecture Flora 2018 (Electronic Edition). Kanagawa Prefecture Flora Survey Association, Odawara. 1803pp. ISBN: 9784991053726

Ohashi, Hiroyoshi; Kadota, Yuichi; Murata, Hitoshi; Yonekura, Koji; and Kihara, Hiroshi. 2017. Wild Plants of Japan (Revised New Edition, Vol. 5: Convolvulaceae to Caprifoliaceae). Heibonsha, Tokyo. 760pp. ISBN: 9784582535358

Paisooksantivatana, Y. 1994. Lycium chinense. In: JS Siemonsma, & K. Piluek (Eds.), Plant Resources in South-East Asia (No. 8 Vegetables, pp. 198-199). Pudoc. ISBN: 9789022010587, http://uses.plantnet-project.org/en/Lycium_chinense_(PROSEA)

Shirataki, Yoshiaki. 2018. Wildflowers of the Mountains and Fields: Edible and Medicinal Properties of Common Wild Plants - Lycium chinense Miller (Solanaceae family). New Food Industry 60(9): 52-54. ISSN: 0547-0277, https://www.i-repository.net/il/user_contents/02/G0000284repository/pdf/JOS-05470277-60(9)-52.pdf

Takatsuki, Shigeki. 2018. Characteristics of fruits used by raccoons—a review. Mammalian Science 58(2): 237-246. https://doi.org/10.11238/mammalianscience.58.237

Takatsuki, Seiki. 2021. Seed dispersal by birds to persimmon trees on the Azabu University campus. Azabu University Journal 32: 1-9. http://id.nii.ac.jp/1112/00005374/

Tanaka, Koji. 1995. Herbal Health Methods: Effectiveness and Usage at a Glance. Kodansha, Tokyo. 123pp. ISBN: 9784061953727

Source

This article is a significantly expanded version of the one included in the following book.

Eggplant (Solanum nigrum) and nightshade (Solanum carolinense) are two species with similar names and flower shapes, so those unfamiliar with them might confuse them. However, eggplant and nightshade are completely different species. Eggplant is a cultivated plant that does not grow wild and has no thorns, while nightshade grows wild and has thorns. However, although eggplant is now thornless, its ancestral species, distributed in South Asia and Southeast Asia, did have thorns. This indicates that the thorns were removed through artificial selection. Not only that, but it is known that its morphology has also been significantly altered by humans. This can be seen as evolution to be convenient for humans, or it can be seen as eggplant "labor parasitism," relying on humans for protection, illustrating the two sides of evolution. The eggplant, thus created, was initially used as medicine mainly in Asia and the Middle East, but after selective breeding reduced its toxicity, its unripe fruit began to be widely used in cooking, including in Europe, Africa, and America. It seems to have been introduced to Japan between the Asuka and Nara periods. On the other hand, the horsetail (Solanum carolinense), native to North America, grows spontaneously, is highly prolific, and is disliked due to its numerous thorns and poison. The flowers of the eggplant and the horsetail are quite similar, and it has been found that the anthers of their stamens are only released when vibrated by a specific type of bee. This is a mechanism to increase the certainty of pollination. The fruit of the horsetail remains poisonous even when ripe, which is a seemingly mysterious phenomenon in nature. There are various theories, but research suggests that it is related to the low nutritional value of the fruit. This article will explain the classification, history, evolution, reproductive ecology, pollination ecology, and seed dispersal of the eggplant and the horsetail.

Two species with names that include "eggplant" and similar flower shapes.

Eggplant (Solanum melongena), also known as eggplant, is a perennial plant believed to originate from eastern India, although there are various theories. In Japan, it is cultivated as an annual. It has been cultivated in Southeast Asia since ancient times (Kodansha, 2013). It gained popularity in the Near East and Asia, and in Japan, it was introduced from China during the Nara period (Aoba, 2013). The unripe purple fruit is mainly used for food (Kodansha, 2013), and the fruit, stem, calyx, root, and flowers were also sometimes used for medicinal purposes (Tanaka, 1995).

Solanum carolinense, also known as the "evil eggplant" or "wild eggplant," is a naturalized plant native to North America that has spread throughout the world. This perennial herb grows in cultivated fields, urban areas, wastelands, and farmlands. Known as a highly invasive weed, it was first recorded in Japan in 1906 (Meiji era) and spread from the early Showa period. Its Japanese name comes from its tendency to proliferate and be difficult to eradicate, as well as the toxicity of its fruit.

Both belong to the Solanum genus of the nightshade family, and their names and flower shapes are similar, so people who haven't seen them before might confuse the two species.

What is the difference between eggplant and nightshade?

However, eggplant and nightshade are completely different species.

Eggplants are cultivated plants and do not grow wild, but nightshade (Solanum carolinense) does grow wild.

In terms of morphology, eggplants have no thorns or stellate hairs on their stems and leaves, whereas horsetails usually have thorns and stellate hairs on their stems and leaves.

Regarding the flowers, eggplants have purple corollas, while horse nightshade (Solanum carolinense) has white to pale purple corollas.

Regarding the fruit, eggplants ripen from purple to yellowish-brown, become elongated and enlarged, and become edible when ripe due to a decrease in solanine content. In contrast, nightshade rhynchophylla ripens from green to orange-yellow, is small and spherical, and contains a large amount of solanine even when ripe, making it inedible.

While eggplant originates from India, nightshade is native to North America. Aside from belonging to the same genus, they are so different that they have almost nothing in common.

Are there any other similar species?

The genus Solanum includes many other species, but only a limited number of them are herbaceous and upright.

For those interested in learning about climbing and woody varieties of the Solanum genus, please see our other article.

What are the differences between Solanum lyratum, Solanum sarmentosum, Solanum sarmentosum, and Solanum jasminoides? We'll explain how to distinguish between similar species! What are the structures of their flowers and fruits?

Solanum lyratum, Solanum sarmentosum, Solanum japonica, and Solanum jasminoides all belong to the Solanaceae family and are four species that share the characteristic of being "climbing plants." Their basic flower and fruit structures are the same, which is why they are often confused. However, these four species have clear differences...

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What are the differences between *Tama coral* (winter coral) and *Himeta coral*? An explanation of how to distinguish between similar species.

Both Solanum sieboldii (winter coral) and Solanum nigrum belong to the Solanaceae family and are cultivated extensively for ornamental purposes because they produce attractive, round, red, ripe fruits (berries) in winter. However, in Japan, it is not always possible to properly distinguish between the two varieties, Solanum sieboldii and Solanum nigrum...

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What are the differences between *Solanum nigrum*, *Solanum sibiricum*, *Solanum nigrum*, and *Solanum nigrum*? We'll explain how to distinguish between similar species!

Black nightshade, large black nightshade, American black nightshade, and glossy black nightshade all belong to the Solanaceae family and Solanum genus. They are very commonly seen in urban areas, and can even be found in green spaces in large cities. They are characterized by their round, black, ripening fruits, but the four species are very similar...

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How did eggplants evolve? Did eggplants originally have thorns?!

How did eggplants evolve?

While various theories have been explored over the years, a scientific method called "molecular phylogenetic analysis," which uses genes to study the evolutionary process of organisms, has now been developed, allowing us to measure the closeness of different species more accurately than before.

Similar research using the same methodology has revealed that the species Solanum insanum is the closest relative to the eggplant (Ranil et al., 2017; Aubriot et al., 2018). Therefore, examining this species may provide insights into how the eggplant evolved.

Since Solanum insanum is a recently separated species, its distribution is not yet fully understood, but it has so far been found in South Asia (Pakistan, India, Sri Lanka), Southeast Asia (Thailand, Laos, Cambodia, Myanmar, Indonesia, Philippines), China, Taiwan, and Madagascar.

From this, it is certain that South Asia and Southeast Asia are the origins of the eggplant. However, isolated distributions such as Madagascar are also observed. This is thought to be due to artificial introduction for cultivation.

What are the morphological differences between eggplant (Eggplant) and Solanum insanum ?

Solanum insanum has thorns all over the plant, its fruit is small and spherical, and its mesocarp is not spongy. In contrast, eggplant (Solanum nigrum), as mentioned above, has no thorns, its fruit is enlarged, and its mesocarp is spongy.

This means that eggplants were artificially selected from Solanum insanum to have no thorns, large fruits, and a spongy mesocarp.

If eggplants had thorns, people might get injured while growing them, and a more developed fruit and mesocarp would make them more satisfying to eat for humans.

Furthermore, unlike Solanum insanum, modern eggplants have the characteristic that even if multiple flowers bloom on a single pedicel (the part connecting the flower to the stem), only the one at the base will produce fruit (Tanaka, 1995). In other words, they have evolved to concentrate their limited resources into a single fruit.

Furthermore, the decrease in solanine is thought to have occurred during later periods of selective breeding.

To some people, these might seem like only good things. However, the absence of thorns and the reduction in solanine clearly make it harder for the plant to protect itself from predators. In fact, anyone who has grown eggplants will likely agree that they are easily eaten by pests and birds.

In other words, "eggplants evolved to specialize in fruit production, abandoning defenses, based on the premise that they would grow while being protected from predators by humans." This type of evolution is widely known in cultivated plants.

While it's true that modern eggplants lack thorns and are easier to grow, they still require constant attention. This can be seen as a testament to the efforts of ancient people, or perhaps a form of "labor parasitism" on humans. Remembering these things when growing eggplants might give you a sense of the wonders of evolution.

What is the history of eggplants? They weren't originally suitable for eating!?

Eggplants, with a total production of approximately 51 million tons in 2016, are the second most economically important fruit crop in the Solanaceae family after tomatoes (Aubriot et al., 2018). How did eggplants spread throughout the world?

As mentioned above, eggplant was artificially selected and domesticated from Solanum insanum, but this domestication may have occurred in multiple locations (Ranil et al., 2017; Aubriot et al., 2018). These regions are thought to be Southeast Asia and South Asia. Generally, the India-Burma region is considered to have been the center of domestication (Daunay & Janick, 2007). Interestingly, unlike the "mizunasu" that Japanese people eat today, eggplants before the progress of selective breeding had strong toxins such as solanine and were primarily used for medicinal purposes, and it seems that some kind of processing was necessary even if they were to be eaten.

In India, various words related to eggplant are recorded in Sanskrit texts dating back to around 300 BC (Mauryan dynasty), suggesting that it was widely used as food and medicine (Daunay & Janick, 2007). In Ayurveda, a traditional Indian and Sri Lankan system of medicine based on Sanskrit, the white fruit is recommended for diabetic patients, and the root for treating asthma. On the other hand, in the ancient Hindu scripture "Marukandeyā Purana" from the 4th century (Gupta dynasty), eggplant is listed among the undesirable. In modern Indian cuisine, eggplant dishes such as achar and beguni are well-known.

In China, it was used as a vegetable crop from an early period, and its existence is shown in the oldest botanical treatise , "Nanfang Caomuzhang, " written by Ji Han during the Western Jin dynasty (265-316), and in the agricultural treatise "Qi Min Yao Shu," written by Jia Sixie during the Northern Wei dynasty around the 6th century (420-581). In "Bencao Gangmu," a comprehensive work of Chinese herbal medicine completed in 1578, Li Shizhen states that medicinal preparations using the fruit, receptacle, roots, stems, and leaves can cure various diseases such as abscesses, intestinal bleeding, and toothaches. In modern Chinese cuisine, it is known to be used in dishes such as Yu Xiang Qiezi (fish-fragrant eggplant).

It is believed that eggplant was introduced to Japan around the 8th century, when the number of Japanese envoys to Tang China increased and relations with Tang China deepened. The oldest documented record is often said to be the "Shosoin Documents of Todai-ji Temple" (750 AD), but it already appears in the "Wooden Tablets of Prince Nagaya's House" (circa 710 AD) (Morishita, 1999). 710 AD was the year the capital was moved from Fujiwara-kyo to Heijo-kyo, marking the end of the Asuka period and the beginning of the Nara period. The "Wooden Tablets of Prince Nagaya's House" mention its use in pickled eggplant, and the "Engishiki," a legal code summarizing the detailed regulations of the Ritsuryo system compiled in 927 AD (mid-Heian period), indicates that it was eaten raw, pickled in soy sauce, pickled in rice bran, and dried. Initially, it was used as a gift for high-ranking individuals, but it became widely cultivated from around the Edo period and finally became a vegetable familiar to ordinary people. Currently, some well-known Japanese dishes include shigi-yaki, asazuke, mapo nasu, nasu dengaku, yakinasu, nasu miso stir-fry, and nibitashi.

Eggplants spread to Persia (present-day Iran) in the western part of the Eurasian continent very early, although the exact time is unknown. Ibn Sina, a scholar of the Samanid dynasty and considered one of the greatest intellectuals produced by the Islamic world, appears in his magnum opus "Canon of Medicine," completed in 1020, which combines ancient Arabic medicine with medical knowledge from Greece and India. Subsequently, it was mentioned by leading medical and botanical writers of medieval Persia, who stated that its toxicity could be reduced by salting and that the fruit could be used to neutralize bile and treat ear diseases.

Its arrival in Europe was late, and for a long time it was unknown in ancient Greece and Rome. However, with the arrival of Muslims in the 7th and 8th centuries, it spread along the Mediterranean coast and eventually reached Europe. However, it did not become popular until the 15th century (Santich & Bryant, 2008=2010). This may be due to its toxicity, but it also seems that one of the reasons is that it is originally a tropical plant and difficult to cultivate (Kodansha, 2013). In current Mediterranean cuisine, in addition to ratatouille, a French dish that is also well-known in Japan, there are eggplant jams (Turkey), baba ghanoush (Levant), ajapsandari (Georgia and Armenia), moussaka (Greece), caponata (Italy), tumbet (Spain), and pisto manchego (Spain).

From the 8th century onward, it was introduced to East Africa by Persian and Arab sailors. During the Age of Discovery (15th-17th centuries), it was transported from Spain to the Americas as one of the vegetables, and by the mid-17th century, it had been reported in Brazil.

What are the health benefits of eggplant?

Eggplant fruit is mostly water (over 931 TP3T), and is low in calories compared to other vegetables. This is one reason why it might not be highly rated, but on the other hand, it is also rich in dietary fiber, making it ideal for dieting.

Although it is sometimes said that it contains almost no vitamins, it does contain a balanced amount of vitamins such as vitamin B2 and vitamin C, as well as minerals such as potassium and calcium, albeit in relatively small amounts.

Studies that have comprehensively examined the health benefits of eggplant have cited the following examples (Fraikue, 2016; Gürbüz et al., 2018). While there are still many unknowns, such as how much eggplant is beneficial to consume and how it compares to other foods, avoiding excessive consumption will likely make it an important source of nutrients that helps the body.

• As an iron chelating agent, eggplant is strongly recommended as a food for pregnant women, breastfeeding mothers, and teenage girls in particular. The iron contained in eggplant can improve premenstrual syndrome, amenorrhea, and anemia in pregnant and postpartum women.
• Because dietary fiber has the property of absorbing harmful chemicals and toxins, it suppresses the proliferation and development of cancer cells.
• The component called nasunin (anthocyanin) has the effect of removing iron accumulated in the body, thus helping to normalize and control iron levels. In addition, nasunin protects humans from lipid peroxides.
• By removing harmful free radicals, relaxing blood vessels in the heart, and ultimately strengthening blood circulation, eggplant helps reduce cardiovascular diseases (stroke, cardiac arrest, and heart disease). Rich in dietary fiber, potassium, vitamin B6, and flavonoids, eggplant reduces the risk of these diseases.
• Ingesting it has the effect of lowering cholesterol. Chlorogenic acid acts as a major antioxidant, and the abundant dietary fiber promotes the absorption of blood cholesterol in order to produce bile in the liver.
• Potassium helps maintain electrolyte balance and assists in neutralizing sodium, which is necessary for blood pressure control; therefore, consuming potassium can help control blood pressure.
• Dietary fiber adds bulk to food, keeping you feeling full for a long time, so it can be used for weight loss.
• It keeps hair, nails, and skin healthy. The high levels of moisture, vitamins, minerals, and fats it contains improve the quality of hair, nails, and skin, and enhance general bodily functions, including resistance to skin cancer.
• High levels of alpha-glycosidase and angiotensin help absorb glucose in the body and, along with other nutrients, control type 2 diabetes. Additionally, phenol-rich extracts assist with the enzymes and glucose assimilation necessary for controlling diabetes. Furthermore, it is low in carbohydrates, and its dietary fiber helps control blood sugar levels.
• Consuming large quantities can prevent damage to brain cells. It also contains plant-based nutrients that enhance memory function and protect cell membranes.
• Because it contains minerals that humans need, such as magnesium, manganese, potassium, and copper, it promotes bone health.
• Dietary fiber flushes out waste products and harmful toxins, promoting healthy digestion.
• It contains antioxidants that protect brain cells, shield them from free radical damage, and help prevent brain tumors, while also maintaining mental health. The chlorogenic acid and phenolic substances it contains act as antiviral, antimutagenic, and antimicrobial agents, helping to supply gentle antibodies to control a healthy life.
• The dietary fiber it contains stimulates bowel movements, cleanses away harmful toxins, and prevents constipation.

Why is the horse nightshade disliked?

While eggplants have been so widely used by humans, the opposite is true of the nightshade (Solanum carolinense). As its name suggests, it's treated as a villain. Why is that?

Its reproductive capacity is high, it has spread to various environments around the world, it is difficult to eradicate, it has thorns, and the entire plant, including the fruit, is poisonous (Miyazaki et al., 2011).

Its native habitat is the United States and Canada, but it has spread to Haiti, Brazil, Bangladesh, Georgia, India, Nepal, South Korea, Japan, Croatia, Norway, and New Zealand.

The first recorded sighting of Solanum carolinense in Japan was in 1906 (Meiji era) at a ranch in Narita City, Chiba Prefecture, but it is believed to have been introduced mixed in with forage grass seeds imported from overseas. However, it does not appear that this population spread throughout the country.

After World War II (1945 onwards), horse nightshade (Solanum carolinense) was recorded in various locations, suggesting it may have been mixed in with military supplies transported by the occupying forces. In the 1990s, it became widely known as a highly damaging weed in fodder fields. As it is a highly damaging weed to corn, soybeans, and cotton in the United States, it may have originated from imported concentrated feed (feed containing high levels of nutrients such as protein, carbohydrates, and fats, but low in fiber). Currently, its distribution has spread from Hokkaido to Okinawa. However, it has been suggested that the records in Okinawa may be of a different species.

Its habitat is extremely broad, and it grows in areas disturbed by human activity, such as cultivated fields, grasslands, orchards, field edges, roadsides, vacant lots, forest edges, roadside plantings, and riverbanks.

Furthermore, it has a strong reproductive capacity. Solanum carolinense spreads vegetatively by sending out rhizomes that spread vertically and horizontally, producing new shoots from the root system and the underground base of the stem. Therefore, it can sprout from roots underground during tilling, or spread by root fragments being mixed into soil during construction or soil attached to plants. In fact, a study in Kyoto City confirmed clones at a distance of more than 1 km. It is possible that its nationwide distribution is mainly following this route. These characteristics make eradication difficult.

Furthermore, although it may be rare in Japan, as described later, it produces fruit and reproduces by seed dispersal. This is likely necessary to adapt to a new environment by exchanging certain genes with other plants.

Even these issues alone can have an impact on the landscape, but that's not the only problem. The entire plant has thorns, so there's a risk of injury when walking on paths or when manually pulling or cutting it to use the land. This also makes eradication difficult. Furthermore, it can get tangled in harvesting machinery and reduce the space available for livestock to use the grassland.

Another problem is its toxicity. It contains toxins such as solanine and saponin, which are common in the nightshade family. Solanidine, which is produced when solanine is hydrolyzed, is a neurotoxin that inhibits estrase, and if livestock consume it, it can cause symptoms of poisoning such as motor disorders, convulsions, coma, and liver damage including jaundice.

The fact that even within the same Solanum genus, there can be such a wide range of evaluations is a fascinating aspect of biological evolution.

What is the structure of the flowers of eggplant and nightshade?

Eggplants are very common plants, but you may not often see their flowers unless you grow them yourself. They flower from June to September, and the inflorescences are mostly solitary, rarely in the form of reduced racemes. There are hardly any peduncles. One to several flowers with purple corollas, 3 to 5 cm long, bloom downwards on pedicels 1 to 1.8 cm long (Tanaka, 1995). The calyx has star-shaped downy hairs and often has spines about 3 mm long on its outer surface.

Solanum carolinense blooms from June to October. Thick branches emerge from the middle of the stem, bearing 6 to 10 pale purple or white flowers, about 2 cm in diameter, in a cymose inflorescence at the tip. The corolla is shallowly divided into 5 lobes and opens into a saucer shape.

As mentioned above, eggplants have fewer flowers than horsetails in order to concentrate nutrients into a single fruit, but aside from this, the flowers of the Solanum genus, including these two species, share many structural similarities.

The distinctive anthers of the Solanum genus depend on the vibrations of bees!?

The stamens, in particular, exhibit a major characteristic common to the Solanum genus.

This is because the anthers, the pollen-containing part of the stamen, are large and conspicuously yellow, and these anthers taper to a point with a small hole. Such anthers are called "porous anthers" (Shimizu, 2001). What role do these special anthers play?

This is related to the fact that many species in the Solanum genus, including eggplant, perform a special type of pollination called "vibration pollination" (Raju & Rao, 2006). Some bees, such as bumblebees and carpenter bees, land on the large yellow anthers and then vibrate with the muscles in their wings, causing the pollen to fall out through the holes at the tips and be carried away. In this way, the Solanum species can prevent nectar robbing by carpenter bees and other species (the act of drilling holes in the calyx and directly taking the nectar without attaching pollen), and can provide them with only pollen for pollination (Ichikawa et al., 2011). It also helps to limit the visits of insects such as syrphidae and honeybees, which visit the flowers of various other plant species and make pollination uncertain.

The downward-facing flowers likely limit the insects that visit them to bees. Hanging onto downward-facing flowers requires strong legs and the ability to fly, and only certain types of bees possess these abilities.

Furthermore, since Solanum species do not produce nectar, it is thought that they have evolved to specialize in pollinating bees and thus deter butterflies and moths from visiting them.

In this way, the Solanum genus cleverly increased the reliability of pollination by limiting the types of insects that visit its plants.

Specifically, regarding Solanum carolinense, there is a record of the black bumblebee Bombus ignitus visiting in Japan (Ichikawa et al., 2011).

In Pennsylvania, USA, its native habitat, 138 out of 146 insects that visited the flowers were Bombus impatiens, a species of bumblebee (Kariyat et al., 2021). However, in Connecticut, several species of the genus Lassioglosum and Augochloropsis metallica of the family Halictidae are also reported to visit the flowers (Quesada-Aguilar et al., 2008).

Why are there both long and short pistils within the same individual?

It is known that eggplant flowers can have three types within the same plant: those with pistils longer than the pistil, those with pistils of the same length, and those with pistils that are shorter than the pistil (National Agriculture and Food Research Organization, 2006).

Because the length of the style within the pistil varies, flowers where the pistil is longer than the stamen are sometimes called "long-styled flowers," flowers where the pistil is the same length as the stamen are called "medium-styled flowers," and flowers where the pistil is shorter than the stamen are called "short-styled flowers."

Furthermore, it has been revealed that there are two types of flowers in Solanum carolinense: long-styled flowers and short-styled flowers (Quesada-Aguilar et al., 2008).

This characteristic of having different styles is called "heterostyly," and it can be seen in various plants (Watanabe, 2022).

However, even though eggplant and nightshade exhibit heterostyliosis, they differ from other plants in several ways. In other plants, heterostyliosis occurs "in separate individuals," so usually only one style length type is observed within a single individual. In contrast, in eggplant and nightshade, heterostyliosis occurs "within the same individual."

While this condition is sometimes referred to as andromonoecy, it's not entirely accurate.

Heterostyle, which occurs "in separate individuals," is generally thought to be a mechanism to prevent self-pollination.

So, what role does heterostylicity, which occurs "within an individual," play?

There are several hypotheses, but a study conducted in Connecticut, USA, on Solanum carolinense supports the idea that by changing the length of the pistil in this way, each flower is responsible for dividing the roles of male and female.

In other words, in long-styled flowers, the pistil is longer than the stamens, so the pistil protrudes. This means the pistil gets in the way, preventing bees from effectively pollinating by vibration and thus preventing them from collecting pollen from the stamens. However, when a bee clings to the flower, it can receive pollen from another individual. Therefore, long-styled flowers take on the role of female flowers and produce fruit.

On the other hand, in short-styled flowers, the pistil is shorter than the stamens, so the pistil is buried within the stamens and cannot be pollinated. Instead, there are no obstacles for the bee to move, so it can efficiently vibrate the flower and drop the pollen onto its body. Therefore, short-styled flowers take on the role of the male bee, and are dedicated to spreading pollen to other individuals.

Interestingly, it has been found that this effect is only exerted when a species of bumblebee , Bombus impatiens, visits.

In Connecticut, it is known that other bees of the family Halicidae also visit the flowers of Solanum carolinense. However, Bombus impatiens touches the flower more frequently and more often with shorter vibrations than other Halicidae bees, efficiently dispersing pollen. This is likely why the difference in pollen dispersal efficiency between long-styled and short-styled flowers is so clearly reflected in the numbers.

I mentioned that eggplant and nightshade flowers come in three types, but it's important to know that they don't always have all three types; some plants only have one type, and there's a lot of individual variation.

This suggests that there are situations where it is beneficial to induce heterostyly growth, and situations where it is not, depending on the type of bee that visits. It is possible that the presence of bumblebees in the environment is closely linked to the occurrence of heterostyly growth "within the individual plant."

As research into the effects of these pollinating insects on plants progresses, we will likely gain a more general understanding of why some plants have heterostyly structured stigmas while others do not.

What is the structure of the fruit of eggplant and nightshade?

The fruits of the Solanum genus are all berries.

Eggplants are classified as berries, but unlike tomatoes, which belong to the same genus, they are not sweet. They are black to purple in color, turning yellowish-brown when fully ripe. Their shape and size vary greatly depending on the variety, but most are over 6 cm in diameter. The seeds are lenticular and yellowish.

The berries of the horsetail plant are spherical, about 1.5 cm in diameter, and ripen from green to yellow.

Eggplant fruits have evolved to be large enough to be eaten, but what is their structure like?

The eggplant fruit has a nested structure consisting of the exocarp, endocarp, partition, placenta, and core (Wang et al., 2021; Nakamura, 2021).

The outermost purple part of an edible, unripe fruit is called the "exocarp." The exocarp contains about four types of anthocyanins, 90% of which is nasunin, a monoacyl anthocyanin, and is the main component that creates the purple color (Ito et al., 2013).

The inside is entirely white and spongy, making it difficult to accurately identify with the naked eye.

Inside the outer pericarp is a thick, fleshy endocarp. Inside the endocarp are multiple placentas, separated by septa, and each placenta contains numerous seeds. These multiple placentas surround the core of the fruit, known as the "pith."

How does the nightshade plant disperse its seeds? Why do some animals eat its poisonous fruit?

It's safe to assume that eggplant seeds are now dispersed by human hands, as mentioned above.

How does the horse nightshade disperse its seeds?

While there are no observations that specifically record the types of animals that eat the fruit, studies in North America suggest that birds and mammals eat the fruit (Cipollini & Levey, 1997a). However, in Japan, there has been an experiment where the fruit of Solanum carolinense was placed and observed with an infrared camera, but no animals that eat it were identified (Miyazaki et al., 2011). However, I have seen Solanum carolinense growing in isolation in a planted area along a road. This could be because the roots of Solanum carolinense were mixed in with the transplanted soil, but it is also possible that the fruit is being eaten by birds.

By the way, there's a big question about the fruit of the horsetail plant. As mentioned above, the fruit of the horsetail plant contains solanine even when ripe and is poisonous. This isn't true for all plants in the Solanum genus; often, the solanine disappears when the plant ripens. So why do such unpalatable fruits exist even when ripe?

This inexplicable phenomenon has been studied in detail (Cipollini & Levey, 1997a; b).

The first possibility to consider is that the toxicity may be limiting which animals come to the fruit. This fruit is toxic to humans, and it is known that ingestion by livestock can cause motor disorders, convulsions, coma, and jaundice. On the other hand, it may be harmless to birds and some wild mammals that digest only the pulp without destroying the seeds, or because their metabolism is different. In this case, it would be possible to get only specific animals to eat the fruit and disperse the seeds. This type of hypothesis is called the "directed toxicity hypothesis."

To verify this, four species of frugivorous birds common in North America—the Japanese robin (Turdus migratorius), the bobtail quail (Colinus virginianus), the mammals Peromyscus maniculatus and Didelphis virginiana— were actually given the fruits of Solanum carolinense (a type of nightshade) along with the non-toxic fruits of Solanum americanum, and their feeding rates were compared.

As a result, all mammals and birds disliked the fruit of Solanum carolinense, which is more poisonous than Solanum nigrum, and their consumption rates were significantly lower. This suggests that the possibility of it being non-toxic to only certain animals, as suggested by the direct toxicity hypothesis, is unlikely.

If that's the case, what other reasons could there be? There are two more hypotheses that consider the relationship with the nutritional value of the fruit.

The first hypothesis is the "Removal Rate Hypothesis." If there are few birds or mammals in the habitat, or if the fruit is relatively less nutritious than other plants and therefore unpopular, the fruit will remain attached to the plant indefinitely. In that case, the fruit is more likely to be damaged by pests or fungi. If that is the case, the benefit of repelling these harmful creatures with its toxicity outweighs the disadvantage of not being eaten by animals that contribute to seed dispersal.

Conversely, if the habitat has many birds and mammals, or if the fruit is relatively more nutritious and popular than other plants, the fruit will be quickly eaten by birds and mammals, eliminating the need to protect it from pests and fungi. In this case, reducing toxicity would have the advantage of being eaten by animals that contribute to seed dispersal, outweighing the disadvantage of not being able to repel harmful pests and fungi.

Simply put, if the rate at which the fruit is eaten is low, the toxicity will be high, and if the rate at which it is eaten is high, the toxicity will be low.

The second hypothesis is the "Nutrient-Toxin Titration Hypothesis," which presents a contrasting perspective. If a plant is highly nutritious and popular with birds and mammals, it may be able to invest in increased toxicity to protect itself from pests and fungi. On the other hand, if a plant is low in nutritional value and unpopular with birds and mammals, it may not attract them at all unless its toxicity is also low.

In short, this hypothesis states that if the rate at which the fruit is eaten is high, the toxicity will be high, and if the rate at which it is eaten is low, the toxicity will be low.

Both arguments seem convincing, but this can only be confirmed by actually conducting an experiment.

This was also tested in the same study that investigated the direct toxicity hypothesis. The results showed that the fruit of the highly toxic Solanum carolinense was not particularly nutritious. This supports the "removal rate hypothesis."

In summary, due to factors such as the scarcity of birds and mammals in its habitat, and the relatively low nutritional value of its fruit compared to other plants making it unpopular, the carnation fruit needed to be protected from pests and fungi for extended periods, and even if it was disliked by birds and mammals, it increased its toxicity.

As mentioned above, the horsetail plant is specialized to grow in barren land, so it may have been difficult for it to sufficiently increase the nutritional value of its fruit. Therefore, as a last resort, it likely protects its fruit with glycoalkaloids such as solanine. Although it is sometimes treated as a villain because it is poisonous, knowing these circumstances on the part of the horsetail plant gives it a different perspective.

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Source

This article is a significantly expanded version of one included in the following book.