Abstract
Impatiens tanintharyiensis Ruchisansakun, Suksathan & Saw-Lwin from the Tanintharyi region of Southern Myanmar is described and illustrated as a new species. The presence of connate lateral united petals and a four-locular ovary, as well as results of molecular phylogenetic analyses of nuclear ITS and plastid atpB-rbcL spacer DNA sequences, suggest that the new species is a member of Impatiens section Semeiocardium (Zoll.) S.X. Yu & Wei Wang. The new species is morphologically most similar to I. spectabilis Triboun & Suksathan, but can be distinguished by its asymmetric flowers, saccate-bucciniform lower sepal, and shorter, slightly incurved spur. Floral traits, including the presence of a large floral chamber with a wide entrance, are consistent with the bee-pollination syndrome in Impatiens. Since I. tanintharyiensis is only known from two small populations, its conservation status is assessed as Endangered.