Polygonum hydropiper L. (family Polygonoceae) is a member of a genus of some 175 species. It is a semi-erect (25–75 cm) annual herb with a branched stem and lance-shaped leaves, carrying its greenish-pink flowers in slender racemes (Fig. 1). The species is widespread in most parts of Europe, temperate Asia, and North America, and it also occurs at scattered sites in North Africa. Across its main range it is abundant in the verges of ponds and ditches and on waterlogged grasslands and water meadows. P. hydropiper is not grown commercially but has found an exceptionally impressive range of uses in folk medicine and also as a culinary herb, and this has led to the adoption of a rich variety of apt local names, e.g. fireweed, arsemart and smartweed are examples of some 20 English regional names in addition to the accepted vernacular name of “water pepper”. The flower heads have little odour but all the aerial parts have a bitter acrid taste and contain vesicant compounds that blister the skin upon repeated handling (Clapham et al. 1952).
