- Family: Buttercup Family – Ranunculaceae
- Growing form: Perennial herb.
- Height: 10–40 cm (4–16 in.). Stem usually arching–ascending, occasionally erect, sparsely branched, usually rooting from basal nodes, almost glabrous.
- Flower: Corolla regular (actinomorphic), yellow, shiny, 8–18 mm (0.32–0.72 in.) wide; petals 5, longer than sepals. Sepals 5, hairy, falling early. Stamens many. Gynoecium separate, with many pistils. Flowers solitary or several together.
- Leaves: Alternate, basal leaves withering early, long-stalked, stalk wide-based, stem leaves short-stalked–stalkless. Basal leaf blades ovate–lanceolate, with entire or toothed margin. Stem leaf blades linearly lanceolate, with entire margins.
- Fruit: Elliptic, round, glabrous, 1.7–2.3 mm (0.68–0.92 in.) long achene, tip with 0.2–0.3 mm (0.008–0.012 in.) long bristle. Achenes often together.
- Habitat: Ponds, puddles, shores, stream banks, ditches, springs, flood-influenced swamps, accretions. Especially in clay-rich ground.
- Flowering time: June–August(–September).
Members of genus Ranunculus grow in a host of different places: from water to dry meadows and from broad-leaved forests to fell-tops. The genus’s real home is probably however in wetlands: Ranunculus means ‘little frog’. Lesser spearwort’s species name flammula comes from the Latin word flamma, which means ‘flame’, and it’s true that the plant’s yellow flowers shine like fire in what is often otherwise a fairly uniform sea of green. Apparently the name however comes from the plant’s fiery flavour: the plants protect themselves against predators with toxins that irritate the skin and mucous membrane. The degree of toxicity varies from species to species, and some are even suitable for the dinner table!
Lesser spearwort is a weak competitor and is rare in the wild. It is usually found near lightly wet swamps, springs and forest streams. It has however moved from its native habitats to cultural areas that have been influenced by people and has benefitted from drainage systems and other modifications to wetlands. A depression in a seldom-walked path or a track for heavy forest machinery suits it wonderfully.
Lesser spearwort varies according to its many habitats. The delicate, small-flowered plants are very difficult to distinguish from its close relative creeping spearwort (R. reptans), but its achene has a smaller bristle and they have different habitats. Creeping spearwort thrives in wavy and sandy lake shores.