Two new species of Begonia L. (Begoniaceae) from central Laos

Begonia comprises at least 1850 species, most of which are local endemics. The greatest genus diversity is observed in tropical zone of America and Asia with particular rich area in Indochinese Peninsula. Meanwhile, the inventory of the genus in this region remains far from acceptable completing. Until recently, only 20 species were documented in Laos. Two more species are described here. Both are local endemics found in small sporadic limestone formations in central Laos. The first species, B. quadripetiolata (expectedly sect. Platycentrum) is endemic of Vientiane province (yang Vieng district). In morphology of staminate flowers, it allies to B. subhowil described from southeastern Yunnan. From B. suhhowii and related B. howii, new species differs in larger leaves, entire leaf margin, leaf petiole quadrate in cross section and very small, caducous inflorescence bracts. Leaf petiole quadrate in cross section, is unique character in the genus. The second species, B. tatianae (sect. Diploclinium) named after its discoverer and grower Mrs. Tatiana Maisak, allies to B. cladotricha, B. gesneriilblia and B. hirmainnoensis originated from limestone formations associated with Hin Nam No Nature Protected Area (central Laos and Vietnam). From allied species, our plant differs in miniature habit, glabrous leaves above dark green, with large diffuse white spot (with small white crystalloid bodies), few stamens, pistillate flowers normally having 4 tepals and ovary bearing wings of distinctly unequal size. Both described species represent characteristic native element of aboriginal limestone flora of lowland karstic formations in central part of Laos.