- Name also: Buckbean, Bog Bean, Buck Bean, Marsh Trefoil
- Family: Bogbean Family – Menyanthaceae
- Growing form: Perennial herb. Rootstock long and thick, creeping or floating.
- Height: 20–40 cm (8–16 in.). Stem glabrous.
- Flower: Corolla regular (actinomorphic), white, outer surface light reddish, 14–16 mm (0.56–0.64 in.) broad, fused, slightly funnel-shaped, inner surface densely fringed, 5-lobed, lobes sharp-tipped, recurved. Calyx with 5 (occasionally 6) lobes. Stamens 5, violet. Gynoecium composed of 2 fused carpels. Inflorescence a raceme.
- Leaves: Alternate, long-stalked, usually only 2–3. Blade with 3 leaflets, leaflets stalkless, elliptic–obovate, with entire margins, glabrous.
- Fruit: Spherical, 1-parted, many-seeded capsule.
- Habitat: Wet swamps, bog ditches, ditches, edges of overgrown ponds and lakes.
- Flowering time: June–July.
Bogbean is often linked in people’s minds with clovers (Trifolium), even though they share nothing in common except having three leaflets. The easiest way to differentiate between them is by the flowers: clover’s are butterfly-like, as is typical of the Pea family, and bogbean’s are completely different. Bogbean actually has two types of flower: one with long style and short stamens and with short style and long stamens protruding from the flower. This arrangement promotes cross-fertilisation because long-stamened flowers’ pollen can only fertilise long-styled flowers, and vice versa. Pollination is carried out by bumblebees and other bees, which are attracted to bogbean’s beautiful flowers. Flowering bogbean is a beautiful sight: the fringed hairs on the inner side of the corolla make the flower very decorative. The job of the hairs is probably to protect the flower’s store of nectar from small insects, which are useless from the point of view of pollination. Seed production varies: a broad stand can be one and the same vegetatively-spreading plant whose seeds never ripen at all.
Bogbean’s flowers only decorate very wet and sunken places – it might even grow in water. The plant floats on the surface with its porous rootstock. If the area dries out or gets covered with bog moss, bogbean gradually stops flowering, although it will grow for a long time with just leaves. Open bogs in the north offer bogbean the most favourable conditions, although the number of suitable habitats decreases in northernmost Lapland and towards the south, and they are mostly small bog margins, the edges of overgrown ponds, and damp forest hollows. In southern Finland the species has disappeared completely due to the drainage of its habitats.
Most Finns nowadays wouldn’t recognise bogbean because it grows in hard-to-reach places. It was familiar to people in the past, however, and in hard times the rootstock was fed to cattle and milled to stretch out flour.