Marsh woundwort (marsh hedge-nettle)
Marsh woundwort is a perennial plant growing from a horizontal tuberous runner. It has square stems with opposite pairs of leaves that are almost stalkless, linearly lanceolate, slightly cordate at the base and toothed. The calyx has five sharply-pointed lobes. The purplish-red flowers are in terminal spikes, with gaps in the lower part of the spike. They are arranged in whorls, each flower consisting of five fused petals, the corolla being two-lipped, the upper lip being gently hooded and the lower lip flat and three-lobed. There are four stamens, two long and two short. The fruit is a dry four-chambered schizocarp.