Derris has been one of the most complex genera in the Millettioid s.str. group. Phylogenetic studies have resulted in the transfer of some species into Aganope and Brachypterum to ensure the monophyly of Derris s.str. However, the Chinese endemic species Derris yunnanensis was not included in these phylogenies. Compared to the other monophyletic genera of the Millettioid s.str. group, this species has received special attention due to its distinctive morphological characters. This paper aims to provide evidence that supports recognition of D. yunnanensis as a separate monospecific genus based on morphology and molecular data including complete chloroplast genome and nuclear ITS/5.8S as well as trnK-matK, trnL-F IGS, and psbA-trnH IGS chloroplast DNA sequences. Derris yunnanensis is consistently recovered in a clade as sister to the genus Antheroporum. The species differs from the other genera of the Millettioid s.str. group by having a pseudoraceme with 6–10 flowers per brachyblast, abaxially puberulent standard, conspicuous calyx teeth with the upper 2 connate and the lowermost distinctly longer than the others, a yellowish-brown puberulent pod having an adaxial suture with a 1–2 mm wide wing, and ovules 3–6 per ovary. Hence, a new genus Ohashia is proposed here.