Taxonomic revision of the genus Myriophyllum (Haloragaceae) in China.
A taxonomic treatment of the genus Myriophyllum from China is presented. The distribution patterns of the species are generalized. Seven species have traditionally been recorded from China: M. aquaticum, M. dicoccum, M. humile, M. spicatum, M. tetrandrum, M. ussuriense and M. verticillatum. Previous identifications of M. humile are incorrect and the species that occurs in China is considered as M. dicoccum. Specimens previously assigned to M. spicatum can be assigned to two distinct taxa, M. spicatum sensu stricto and M. sibiricum. M. alterniflorum, M. heterophyllum, M. oguraense, M. sibiricum and M. tuberculatum are new records for China. Comments, descriptions, additional notes, specimen citations, distribution, diagnoses and a key for the Chinese taxa of Myriophyllum are provided. The native species of this genus exhibit both strong warm/cool temperate affinities and tropical affinities. Four distribution patterns are generalized as follows: Old World Tropics (3 species); Old World Temperate (one species); North Temperate (4 species); and East Asia endemics (one species).