It is a herbaceous perennial plant growing trailing stems to 50-80 cm long, typically on sand and gravel storm beaches. The leaves are waxy glaucous green, 5-10 cm long, pinnate, with 2-5 pairs of leaflets, the terminal leaflet usually replaced by a twining tendril. The flowers are 14-22 mm broad, with a dark purple standard petal and paler purple wing and keel petals; they are produced in racemes of 2-7 together.
The unusually extensive native range is explained by the ability of the seeds to remain viable while floating in sea water for up to 5 years, enabling the seeds to drift nearly worldwide. Germination occurs when the hard outer seed coat is abraded by waves on sand and gravel.
The pods can be eaten but like many members of the genus Lathyrus they contain β-oxalyl-L-α,β-diaminopropionic acid, which can cause paralysis called lathyrism. The leaves of the plant are used in Chinese traditional medicine.
- Lathyrus japonicus 2.jpg
- Lathyrus japonicus 1.jpg