H. vulgaris: stems slender, creeping, rooting at every node, and emitting small tufts of leaves and flowers; leaves obicular, crenate or slightly lobed, attached by the centre to a rather long stalk; peduncles shorter than the leafstalks, with a single terminal head or 2-3 whorls of minute white almost sessile flowers; fruits small, flat, glabrous. - Bogs, marshes, and edges of ponds. Fl. June to August.