Persicaria jucunda var. rotunda (Polygonaceae, Persicarieae), a distinct distylous taxa raised to specific rank

Persicaria jucunda (Meisn.) Migo var. rotunda (Z.Z.Zhou & Q.Y.Sun) Bo Li was originally published in the genus Polygonum L. and treated as a variety of P. rotundum Meisn. [≡Persicaria jucunda (Meisn.) Migo]. After carefully comparing the macro- and micro-morphological characteristics of the achenes, leaf epidermis and tepals and the habitat between the variety and its typical variety, we confirmed that P. jucunda var. rotunda is clearly different from P. jucunda and should not be treated as a variety, but be raised to a specific rank as P. rotunda (Z.Z.Zhou & Q.Y.Sun) Bo Li. The species is distylous and could be easily distinguished from all other Persicaria taxa by a combination of morphological characters, such as completely decumbent leafless basal branches, almost sessile leaves, linear-lanceolate with rounded leaf bases, spicate, short and dense inflorescences, slender pedicels longer than bracts and dimorphic flowers and achenes. P. rotunda is endemic to several large wetlands of eastern China and usually occurs as one of the dominant species in some plant communities.