- Name also: Marsh Hedgenettle, Clown’s Woundwort
- Family: Mint Family – Lamiaceae (Labiatae)
- Growing form: Perennial herb. Rootstock horizontal. With subterraneous runners, runners tuberous.
- Height: 20–100 cm (8–40 in.). Stem often ascending, usually unbranched, hollow, 4-edged, sparsely haired especially along edges, internodes at most slightly longer than leaves. With faintly unpleasant fragrance–almost without fragrance.
- Flower: Corolla irregular (zygomorphic), rose-red, with light-coloured pattern, 12–15 mm (0.48–0.6 in.) long, fused, bilabiate, long-tubed. Upper lip convex, hairy, with glandular hairs, shorter than lower lip; lower lip 3-lobed, central lobe larger than lateral lobes, quite round. Calyx almost regular (actinomorphic), 5-lobed, unclearly 10-veined, lobes sharp-pointed. Stamens 4, of which 2 short, 2 long. Gynoecium composed of 2 fused carpels. Inflorescence spike-like, lower part with long gaps, comprised of dense, axillary whorls.
- Leaves: Opposite, short-stalked–stalkless. Lacking basal rosette. Blade linearly lanceolate, with shallowly cordate–round base, quite light green, hairy, margin regularly shallow-toothed. Inflorescence subtending bracts small.
- Fruit: 4-parted schizocarp. Mericarps slightly bristly, shiny, brown.
- Habitat: Shores, alder swamps, meadows, ditch and stream banks, arable and waste ground.
- Flowering time: July–August.
Marsh woundwort’s handsome flowers attract bumblebees to pollinate it and the nectar indicators efficiently guide it onwards to the stamens and pistils. Although the species makes a great investment in sexual reproduction, it can spread even more efficiently vegetatively. As the growing season progresses, thin subterraneous runners strengthen their tips into long, finger-wide elliptic tubers which survive the winter. The tubers can be eaten young like asparagus and Jerusalem artichoke, and one of its Asian relatives is cultivated in Europe too as food. Marsh woundwort’s tubers are not just a way to get through the winter, they are a means of spreading: the tubers develop air-pockets the runners spread even during autumn rain. The carpels sail along on the water using the calyx as a sail.
Marsh woundwort’s adaptations are the key to it thriving along coasts, and stands can even be found in water. It also thrives in fields, however, and can often be found nowadays growing abundantly on cultivated land and waste ground. It has travelled north with people from its native habitat, where it still returns to the water’s edge. In damp root vegetable and grain fields it can be a persistent nuisance that is hard to get rid of. At its best, however, pink-flowered marsh woundwort has just as much right to be seen as an ornamental as a weed.