Herbs perennial, from rhizome, glabrous or sparsely pubescent. Stems angled to narrowly winged, erect, sprawling, or climbing, basally branched 0–4 times, 1–10 dm. Leaves 3–15 cm; tendrils usually well devel­oped, branched or unbranched; stipules sagittate-ovate, 7–35 × 7–30 mm, as large as basal leaflets; leaflets 6–12, usually scattered, blades ovate to lanceolate, 15–55 × 5–35 mm, surfaces glabrous throughout or pubescent abaxially. Inflorescences 4–9-flowered, 4–15 cm. Flowers 12–29 mm; calyx lobes unequal, lateral lobes linear-triangular, longer than tube; corolla blue to purple, banner erect, blade longer than claw, wings equal to keel; ovary eglandular and glandular-pubescent. Legumes 35–65 × 6–12 mm.

Distribution

North America, Eurasia, introduced in s South America.

Discussion

Varieties 3 (3 in the flora).

Within Lathyrus japonicus, in the narrow sense, there is a south to north reduction in plant size, including plant height, robustness, and leaflet size, but not flower size, flower number, or fruit size. On the east coast of North America this shift seems fairly abrupt, giving the appearance of a clear distinction between var. maritimus and var. pellitus in the south, and var. japonicus to the north in Labrador and Greenland. However, on the West Coast, there are few truly pubescent forms (var. pellitus), and there seem to be many more intermediates between var. maritimus in the south and var. japonicus to the north.

Selected References

None.

Lower Taxa

Lathyrus japonicus var. japonicus, Lathyrus japonicus var. maritimus, Lathyrus japonicus var. pellitus

Key

1	Stems 1–3.5 dm; leaflet blades 15–35 mm; tendrils unbranched, less than 3 cm.	Lathyrus japonicus var. japonicus
1	Stems 3–10 dm; leaflet blades 30–50(–55) mm; tendrils branched, 3+ cm.	> 2
2	Leaflet blades glabrous.	Lathyrus japonicus var. maritimus
2	Leaflet blades pubescent abaxially (especially new growth).	Lathyrus japonicus var. pellitus