Taxonomic revision of the Vitex trifolia complex (Lamiaceae)

The Vitex trifolia complex is a well-circumscribed and monophyletic group. However, the species of the group are morphologically very similar and therefore, taxonomic boundaries within the group are uncertain. In addition, these medicinal plants have been cultivated and naturalised in many areas across the world and therefore their natural geographical distributions are not well known. A taxonomic account of the complex is presented in which nine species are recognized: Vitex agnus-castus, V. benthamiana, V. bicolor, V. negundo, V. pseudonegundo, V. rotundifolia and V. trifolia; a new species, Vitex collium Sengun, is described from frost prone regions of northern and Central China and an obscure name, V. hybrida Moldenke, is recognised for the Indian specimens previously V. negundo f. intermedia, V. negundo f. laxipaniculata, V. rotundifolia and V. trifolia var. acutifolia are lectotypified, and V. leucoxylon Blanco has been neotypified. Also, many names have been placed in synonomy for the first time.