Begonia L. section Diploclinium, as currently circumscribed, contains ca. 150 species and is distributed from India and Sri Lanka, through the Himalayan region, China, Indo-China, Taiwan, Malesia to Fiji. It contains a morphologically diverse group of taxa and is defined largely by having bilamellate placentae and a lack of characters which are diagnostic of other Asian sections. In order to understand the taxonomic position of the Philippine members of the section a thorough study of its morphology was undertaken. Cluster analysis of vegetative and morphological characters shows that the group of Philippine Begonia form a homogenous group. Unlike the other members of sect. Diploclinium, they are morphologically similar to each other. They share characters which include: rhizomatous stem; leaves asymmetric with palmate-netted venation; axillary inflorescence; male flowers basal and female flowers distal; protandrous; 2+2 tepals; placenta with 2 branches; capsule pendulous, 3-locules; wings 3, equal or unequal and bulbils absent. Begonia oxysperma is shown to be best placed with sect. Baryandra which is well differentiated from the type of sect. Diploclinium. Accordingly, B. oxysperma is excluded from sect. Diploclinium. The results of this research highlight the perils of placing high taxonomic importance on single reproductive characters and emphasize the importance of some overlooked vegetative characters.

Key words: Begonia, sect. Diploclinium, sect. Baryandra, species delimitation, Philippines