- Name also: Heath Pea (Note! Bitter vetch is also the English name of Vicia ervilia and sometimes also Vicia orobus).
- Family: Pea Family – Fabaceae (Leguminosae)
- Growing form: Perennial herb. Rootstock with dark tubers.
- Height: 15–30 cm (6–12 in.). Stem erect, winged, fairly glabrous.
- Flower: Corolla zygomorphic, purple, later bluish, 10–16 mm (0.4–0.64 in.) long, Petals 5; the upstanding the ‘standard’, the lateral two the ‘wings’, the lower two united to form the ‘keel’, overall shape of corolla being butterfly-like. Calyx 5-lobed. Stamens 10. A single carpel. Inflorescence a long-stalked, 2–6-flowered raceme.
- Leaves: Alternate, stalked, stipulate. Blade pinnate, 2–4-pairs, lacking tendrils. Leaflets elliptic–lanceolate–linear, blunt, with entire margins. Stipules large.
- Fruit: 25–45 mm (1–1.8 in.) long, glabrous, reddish brown–blackish brown, 6–10-seeded pod (legume).
- Habitat: Broad-leaved forests, herbaceous forests, hedgerows, banks.
- Flowering time: May–June.
Bitter vetch’s tubers, which are quite sweet and nutty-tasting, have undoubtedly been eaten in their time – although they should probably be boiled first as the plant is mildly toxic.
Finland’s climate limits bitter vetch to the south-western corner of the country. Apart from dry broad-leaved forests and young forests, it also grows on relatively barren heaths. It is clearly not dependent on lime, as many other plants that are growing at the northern edge of their climate are. People have probably spread the plant to the north, as it is difficult to explain its fragmented stands in the centre of its northern habitat in Uusimaa, Satakunta and northern Häme in any other way. Bitter vetch usually grows abundantly in a very small area, but it quickly gets rarer away from these focal points for no clear reason. Its connection to Iron Age settlements is so clear that archaeologists use the plant to locate ancient relics. The fact that it grows on the sites of ancient Finnish settlements strongly points to the fact that ancient Finns used it for food or medicine and deliberately transplanted it to new habitats. Large-seeded bitter vetch has troubles spreading very far under its own steam. In recent times it has spread to new habitats e.g. with traffic.
Bitter vetch looks like spring vetch (L. vernus), but the latter’s stems are wingless, its leaves are more ovate and lightly veined, and it is more delicate in general.
Poisonous or not?
It is not recommended to eat bitter vetch’s (heath pea’s) large seeds, the peas: like its relatives and other wild peas they contain poisonous compounds such as allantoin, arbutin and toxic amino acids.
Bitter vetch’s seeds are eaten e.g. in order to lose weight (also eating tubers have had no side effects other than weight loss). The other plant species known as bitter vetch (Vicia ervilia) is proven toi be poisonous: the seeds are edible only if prepared properly (blanched and after that the water must be dumped out several times to ensure that the final dish is not toxic and if one wants to eat seeds more than once.