The family Pontederiaceae consists of emergent, submerged, or floating aquatic plants, which are annual or perennial. The leaves are opposite, linear, or with clearly separated petioles and blades, and the blades are linear, orbicular, or scaly, with entire margins. The flowers are terminal, arranged in conical, umbel, or spike inflorescences, or borne in pairs or singly. The flowers are bisexual, bilaterally symmetrical or nearly radially symmetrical. The perianth segments are usually 6 in number, nearly free or tubular at the base, petal-like, and wilt quickly. The stamens are homomorphous or dimorphic, 6, 4, 3, or 1. The pistil has a superior ovary, 3-chambered, sometimes 1-chambered. The fruit is a capsule or a nutlet (pseudocarp) enclosed at the base of the perianth segments. There are many or 1 seed. There are 9 genera and about 33 species found in tropical to temperate regions worldwide. Two species of the genus Monochoria are native to Japan, while one species each of the genera Hyacinth, Monochoria, and Pontederia have become naturalized.
This article provides a comprehensive, field guide-style introduction to plants belonging to the Pontederiaceae family.
The basic information is based on the Kanagawa Prefecture Flora Survey Association (2018). Photos are replaced as better ones become available. While the identification is done by the author, please note that misidentifications may be corrected without notice.
No. 0636 Water Hyacinth (Eichhornia crassipes)
Also known as water hyacinth, water hyacinth, and water sedge. It is a perennial plant, but can be grown annually in colder climates. The basal leaves grow in clumps. The leaf blades are ovate, 4-10 cm long. The flower stalks are about 20 cm tall and bloom from August to October. The flowers are 3 cm in diameter, and the perianth segments are pale purple. The entire inflorescence blooms simultaneously, then curls back and sinks into the water the following day. Native to tropical America, it has naturalized in Honshu (west of the Kanto region), Shikoku, Kyushu, and the Ryukyu Islands. It overwinters and naturalizes in riverbanks and ponds in various locations. It has been designated as an alien species that causes damage to ecosystems by the Ministry of the Environment (a species of concern before March 2017), and has also been selected as one of the "World's 100 Worst Invasive Alien Species" by the International Union for Conservation of Nature (IUCN) and one of the "Japan's 100 Worst Invasive Alien Species" by the Ecological Society of Japan.
References
Kanagawa Prefecture Flora Survey Association. 2018. Kanagawa Prefecture Flora 2018 (Electronic Edition). Kanagawa Prefecture Flora Survey Association, Odawara. 1803pp. ISBN: 9784991053726
