Systematic revision of the indigenous Begonia sect. Platycentrum in Vietnam

Begonia L. is a genus of ca. 1,500 species distributed throughout the tropics and subtropics, except for northern Australia. Section Platycentrum can be differentiated from the other sections by its large size, thick stems or rhizomes, axillary inflorescences, 4 tepals in the staminate flower, 5 or 6 tepals in the pistillate flower, projecting anther connectives, thick and long fruit wings, bilocular ovaries, and bifid placentae. In Vietnam, Laos and Cambodia, Gagnepain (1921) recognized six species of section Platycentrum from Vietnam, while Pham (1999) also recognized six species from this section. A revision of section Platycentrum in Vietnam, including a key, is presented here. There are detailed descriptions, illustrations, distribution maps, habitat notes and other relevant data for all taxa. Fourteen species are recorded from Vietnam, of which seven species (B. algaia, B. duclouxii, B. hemsleyana, B. laminariae, B. miranda , B. siamensis and B. subhowii ) and three varieties (B. palmata var. khasiana, B. palmata var. laevifolia, and B. villifolia var. australis var. nov.) are reported from that country for the first time.