Lathyrus palustris aka Marsh Pea

Lathyrus palustris is known as marsh vetchling or marsh pea. It is a deciduous perennial in the pea family, Fabaceae. Its native range spans Europe, temperate Asia, and eastern North America. It grows wild in Britain and Ireland. Its range reaches from Norway south to northern Spain. It also extends east through Siberia to Japan. Wild plants grow in fens and other damp places. They grow among grasses or bushes.

This plant can trail along the ground or climb. It reaches about 4 feet [1.2 metres] in height. Tendrils help it grip nearby plants for support. Narrow, spear-shaped leaflets grow in pairs along the leaves. It loses its foliage for winter. Plants reach maturity within one to two years. Its loose growth suits planting among other wet-ground plants. Nearby stems give the tendrils places to hold.

The flowers have the familiar shape of pea flowers. RHS describes them as pink-purple, reaching about 0.07 feet [0.02 metres] across. It gives July to August as the flowering season. Chicago Botanic Garden records a longer season, from May through August. Its listed flower colours include pink, white, blue, and purple. These accounts show some variation in flower colour and timing. The pods and seeds need care around people and pets.

Grow marsh vetchling in soil that stays wet or moist. It accepts full sun or partial shade. RHS lists clay and loam, with neutral or alkaline pH. Poor drainage suits this plant rather than ruling it out. It can also grow in very shallow pond-edge water. Bog gardens, damp wildflower meadows, and wildlife gardens offer suitable settings. RHS rates its winter hardiness as H5. Chicago Botanic Garden lists USDA zones 5–7. Seed provides a means of raising new plants. Routine pruning is not needed; tidy after bloom when needed.

Aphids, slugs, and snails may damage the plant. Possible diseases include powdery mildew, Fusarium wilt, and sweet pea viruses. Plants For A Future records it as a nitrogen fixer. That source reports cooked seeds, young leaves, and stems as food. RHS gives a conflicting warning against eating pods and seeds. It extends that warning to pets and advises protective gloves for handling. Do not treat the food records as proof of safety. Plants For A Future lists no known medicinal uses.