Description from Flora of China
Polygonum [unranked] Persicaria Linnaeus, Sp. Pl. 1: 361. 1753; Persicaria Miller.
Plants without prickles. Leaves generally narrowly elliptical to ovate, not hastate or sagittate. Inflorescence spicate, spikes usually several. Tepals fused for about 1/3 their length. Nectaries free, globular. Styles 1, bifid or trifid.
In members of Polygonum sect. Aconogonon, P. sect. Bistorta, P. sect. Cephalophilon, P. sect. Echinocaulon, and P. sect. Persicaria (often recognized as belonging to the genus Persicaria) the inflorescence is many flowered, the petioles lack articulation, the ocrea is variously entire, ciliate, or pectinate, but not laciniate, the perianth is 4- or 5-parted, the tepals have 3-fid venation, the stamens are 4–8, with reduction in number occurring in the inner whorl, and the filaments are not dilated at the base, but are associated with nipple-like nectaries.
Synonymy updated after publication of Flora volume.
About 100 species: cosmopolitan; 23 species (four endemic) in China.