Seaside Pea (Lathyrus japonicus) — identification, habitat & look-alikes

Seaside pea, better known in the US as beach pea, is a native wildflower that sprawls over sandy beaches and dunes. Its purple, sweet pea–like flowers bloom in summer and are followed by flat pods. Besides ocean beaches, it also grows on the shores of the Great Lakes.

Appearance

Appearance: A sprawling perennial 1–2 ft (30–60 cm) tall, with angled stems that spread from underground runners into dense patches.
Leaves: Each leaf has 3–6 pairs of thick, oval leaflets 1–2 in (2.5–5 cm) long and ends in a branched . A pair of large, arrowhead-shaped sits at the base.
Flowers: Pea-shaped flowers ½–¾ in (1.2–2 cm) long come in clusters of about 3–10. The upper petal is rich purple with darker veins, and the side petals are pale violet to white.
Flowering time: June–August (Minnesota)
Fruit: Smooth, flat pods 1½–3 in (4–8 cm) long.

Look-alikes

Veiny peaLathyrus venosus

Veiny pea is taller (up to 3 ft / 90 cm), carries more than 10 flowers per cluster, and has much narrower stipules with sharp tips. It grows inland, not on beaches.

Why they get mixed upIts flowers look almost identical.

Marsh peaLathyrus palustris

Marsh pea has thin, not fleshy, leaves, narrow stipules with only one lobe at the base, often winged stems, and narrower pods (about ¼ in / 4–7 mm wide).

Why they get mixed upIt is another purple-flowered wild pea of wet, open shores.

Silky beach peaLathyrus littoralis

Silky beach pea is gray-hairy all over, with small, nearly round leaflets only ½–¾ in long and dense heads of 4–8 white-and-pinkish-purple flowers. Beach pea's leaflets are bigger (1–2 in).

Why they get mixed upBoth grow on Pacific coast dunes and have pink-to-purple pea flowers.

Where it lives

Typical habitats: Sandy beaches
Dunes
Sandy and gravelly lakeshores
Brackish and salt marshes
Range: Along the Atlantic coast from New Jersey north to Maine, along the Pacific coast, and around the Great Lakes. It also occurs in Asia and Europe.
Preferred conditions: Sandy or gravelly soil in full sun to part shade, close to large bodies of water.
Flowering: Flowers Jun–Aug
Flowers Jun–Aug

Life cycle

Seed dispersal: The seeds float and can stay alive in seawater for up to five years, which likely explains how the plant spread around the Northern Hemisphere. Waves wear down the hard seed coat, which lets the seeds sprout.

Cautions

Cautions: The pods have been eaten, but like other wild peas in this genus, the plant contains a compound that can cause , a form of paralysis, if eaten in large amounts.

Name and classification

About the name: Several varieties have been named, including Atlantic beach pea (var. maritimus) and downy beach pea (var. pubescens), but they are poorly documented. Older books may call it Lathyrus maritimus.