A new bicarpellate Buxus species, Buxus sirindhorniana W. K. Soh, M. von Sternburg, Hodk. & J. Parn., is described from northern Thailand. This is the first reported bicarpellate species of Buxus . The pollen morphology and the degree of pollen viability of the species are reported. DNA was extracted from herbarium samples and the internal transcribed spacer (ITS) region of nuclear ribosomal DNA sequenced. The palynological evidence and the phylogenetic reconstruction support the contention that this new species belongs to the genus Buxus . The morphological diversity of reproductive organs in the Buxaceae, in relation to this new species, is briefly discussed.