Lathyrus sylvestris aka Narrow Leaf Everlasting Pea

Lathyrus sylvestris is a long-lived climbing plant in the pea family, Fabaceae. Common names include flat pea and narrow-leaved everlasting pea. Its native range spans Madeira, Europe, western Siberia and the Caucasus. It is native to Britain and Ireland. People have introduced it to Canada and the northern United States. It grows in woods, thickets, waste ground and on banks.

This deciduous perennial climbs with tendrils or scrambles across the ground. Garden plants reach about 5–8 feet [1.5–2.5 metres] tall with support. Without support, they may stand around 2.5 feet [0.76 metres]. RHS gives a spread of 1.6–3.3 feet [0.5–1 metre]. NC State reports spreads near 6.6 feet [2 metres]. Rhizomes let established plants form mats that crowd out other plants. Green stems are flat, floppy and edged with broad wings. Alternate, pinnate leaves have narrow green leaflets and a terminal tendril. RHS describes paired, lanceolate leaflets reaching 0.5 feet [0.15 metres] long.

Flowers appear in summer and can last into early autumn. Long stalks carry racemes of about three to ten blooms. Their pink to rose-pink petals may show green and purple marks. Each flower measures up to 0.07 feet [0.02 metres] long. The fruit is a flat legume that turns black. Pods measure about 0.17 feet [0.05 metres] and hold five to fifteen seeds. Birds eat the seeds.

Grow it in sun or light shade with good drainage. RHS recommends fertile soil, though NC State records tolerance of poor ground. It accepts clay, loam, sand and chalk across a broad pH range. Moist soil suits it, but established plants withstand drought. RHS rates it H6; NC State lists USDA zones 2a–9a. Growth is moderate, and plants need little care once established. Train stems onto supports or let them scramble through borders. Remove spent flowers to extend bloom, then cut back in autumn. Propagate it from seed.

Gardeners use flat pea on walls, banks and in informal borders. It also provides soil cover, fixes nitrogen and helps curb erosion. Watch its spread: NC State warns that it can become invasive. Aphids, slugs and snails may attack it. RHS also lists powdery mildew, Fusarium wilt and sweet pea viruses. Do not treat its pea-like pods as food. RHS warns that pods and seeds are unsafe for people and pets. Large amounts can cause lathyrism, a serious nerve disease. PFAF records no known edible or medicinal uses.