All species of the Polygalaceae family found in Japan are herbaceous. Their leaves are simple, alternate, and lack stipules. Flowers are bisexual and bilaterally symmetrical. They have 5 sepals and 5 petals, some of which are reduced or fused. Stamens are 4 or 8, fused at the base. The ovary is superior and 2-chambered. Fruits are capsules or drupes. Approximately 1,000 species across 17 genera are known from tropical to temperate regions, excluding the Western Pacific. In Japan, 13 species across 2 genera are known, including naturalized species.
This article provides a comprehensive, field-guide-style introduction to the Polygalaceae family.
The photos are replaced as soon as better ones are taken. Also, while the identification is done by the author, please note that if there are any misidentifications, they may be changed without notice.
No. 1617 Polygala japonica
This evergreen perennial herb (Kanagawa Prefecture Flora Survey Association, 2018). The stem is rigid, branching at the base and creeping along the ground, with the tip growing obliquely upward to a height of 10-30 cm. The leaves are almost sessile, ovate or oblong, 1-3 cm long and 4-15 mm wide, with sparse, curved fine hairs on the midrib. The raceme is borne opposite the leaves in the leaf axils of the upper stem, with reddish-purple petals that appear as three, some of which are reduced or fused, and the lower petals have a tufted appendage at the tip. The capsule is flattened and heart-shaped, 7-8 mm in diameter, and is sandwiched between two persistent lateral sepals. It is distributed in Hokkaido, Honshu, Shikoku, Kyushu, Okinawa; Korea, China, and Southeast Asia. It is commonly found in sunny grasslands, but its population is declining around urban areas. The seeds have elaiosomes and are dispersed by ants (Fujii et al., 2012; Nakanishi, 1999; Nakanishi et al., 2021).
References
Fujii, M., Kosaka, A., & Masui, K. 2012. Plants that rely on ants to disperse their seeds. Kyosei no Hiroba 7: 63-68. ISSN: 1881-2147, https://www.hitohaku.jp/publication/book/kyousei7_063.pdf
Kanagawa Prefecture Flora Survey Association. 2018. Kanagawa Prefecture Flora 2018 (Electronic Edition). Kanagawa Prefecture Flora Survey Association, Odawara. 1803pp. ISBN: 9784991053726
Nakanishi, Hiroki. 1999. Seed dispersal by ants. pp. 104-117. Ueda, Keisuke (Ed.), Seed dispersal: The Evolution of Mutual Aid Vol. 2: Forests Created by Animals. Tsukiji Shokan, Tokyo. ISBN: 9784806711933
Nakanishi, Hiroki; Kadota, Yuichi; and Chijibu, Yoshiro. 2021. A new naturalized plant of the Polygalaceae family found in Japan, *Polygala japonica* (new name). *Phytogeography and Taxonomy* 69(1): 99-101. https://doi.org/10.18942/chiribunrui.0691-14
