Persicaria is a genus of herbaceous flowering plants in the knotweed family, Polygonaceae. Plants of the genus are known commonly as knotweeds or smartweeds. It has a cosmopolitan distribution, with species occurring nearly worldwide. The genus was segregated from Polygonum. Description The genus includes annual and perennial herbs with taproots or fibrous root systems, or with rhizomes or stolons. The stems are often erect but may be prostrate along the ground, and some species are prickly. The stems are self-supporting or twining and climbing. The leaves are alternately arranged, deciduous, and variously shaped. The brownish or reddish ochrea may be leathery to papery. The inflorescence may be a panicle or a spikelike or headlike arrangement of fascicles of flowers. The flower is white, greenish, reddish, pink or purple, with the tepals partially fused together along the bases. The fruit is an achene which can take a number of shapes, including a disc or a sphere. Taxonomy Within the family Polygonaceae, Persicaria is placed in the subfamily Polygonoideae, where the tribe Persicarieae consists of two sister genera, Bistorta and Koenigia, together with Persicaria. Species , Plants of the World Online accepted the following 131 species: Persicaria acuminata (Kunth) M.Gómez Persicaria akakiensis (Cufod.) Soják Persicaria amphibia (L.) Delarbre – amphibious bistort, water smartweed Persicaria angustifolia (Pall.) Ronse Decr. Persicaria arifolia (L.) Haraldson – halberd-leaf tearthumb Persicaria assamica (Meisn.) Soják Persicaria attenuata (R.Br.) Soják Persicaria barbata (L.) H.Hara Persicaria biconvexa (Hayata) Nemoto Persicaria bicornis (Raf.) Nieuwl. – pink smartweed Persicaria breviochreata (Makino) Ohki Persicaria bungeana (Turcz.) Nakai – prickly smartweed Persicaria capitata (Buch.-Ham. ex D.Don) H.Gross – pink-head knotweed Persicaria careyi (Olney) Greene – Carey's smartweed Persicaria cespitosa (Blume) Nakai Persicaria chinensis (L.) H.Gross – Chinese knotweed Persicaria debilis (Meisn.) H.Gross ex W.Lee Persicaria decipiens (R.Br.) K.L.Wilson – slender knotweed, willow-weed Persicaria dichotoma (Blume) Masam. Persicaria dissitiflora (Hemsl.) H.Gross ex T.Mori Persicaria eciliata M.A.Hassan Persicaria extremiorientalis (Vorosch.) Tzvelev Persicaria ferruginea (Wedd.) Soják Persicaria filiformis (Thunb.) Nakai Persicaria foliosa (H.Lindb.) Kitag. Persicaria galapagensis (Caruel) Galasso Persicaria glabra (Willd.) M.Gómez' – smooth smartweed Persicaria glacialis (Meisn.) H.Hara Persicaria glandulopilosa (De Wild.) Soják Persicaria glomerata (Dammer) S.Ortiz & Paiva Persicaria hastatosagittata (Makino) Nakai Persicaria hirsuta (Walter) Small – hairy smartweed Persicaria hispida (Kunth) M.Gómez Persicaria humilis (Meisn.) H.Hara Persicaria hydropiper (L.) Delarbre – water-pepper, marsh-pepper smartweed Persicaria hydropiperoides (Michx.) Small – swamp smartweed, mild water-pepper Persicaria hystricula (J.Schust.) Soják Persicaria japonica (Meisn.) Nakai Persicaria kawagoeana (Makino)