Three new taxa of Begonia (sect. Coelocentrum, Begoniaceae) from limestone areas in Guangxi, China

Begonia ningmingensis, B. ningmingensis var. bella and B. retinervia, three new taxa of B. sect. Coelocentrum from the karst area in Guangxi Zhuangzu Autonomous Region, China, are described and illustrated. Notably, their leaves are adorned with white or pale maculation along all major veins. Begonia ningmingensis var. ningmingensis resembles B. morsei Irmsch., differing by having larger leaves with white maculation on the major veins and having larger staminate flowers. The maculation pattern in the leaves of B. morsei is sharply distinct: they are adorned with a broad, white ring between the center of the leaf and the margin. Begonia ningmingensis var. bella differs from the typical variety mainly by the suborbicular or reniform leaves with a rounded or obtuse apex (vs. broadly ovate or suborbicular with an acuminate, shortly acuminate or acute apex). Begonia retinervia is distinct chiefly by having thickly chartaceous leaves, the broadly trigonous-ovoid or obovoid ovary and fruit covered with crisp-villous hairs, and the ventral surface markedly convex, and in the much protruded abaxial wing.