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A novel species of Rhamnaceae, Colubrina zhaoguangii, is discovered in Sichuan, China, during the biodiversity investigations of the Second Tibetan Plateau Scientific Expedition and Research. Detailed descriptions and illustrations of the new species are presented herein. To date, the new species is only found in dry-warm river valleys of the Jinsha River basin in the Hengduan Mountains region (HDM). Compared with the other two known Chinese Colubrina species, C. zhaoguangii features by the habit of twisted shrub and tiny leaves with emarginate apex. In morphology, the new species highly resembles C. alluaudii endemic in Madagascar and C. viridis in northwestern Mexico, whereas it is distinguished from these two relatives by its minutely white scales on the leaf blades. The discovery of C. zhaoguangii reminds us again that the bottom region is also important for biodiversity conservation in HDM and should be a flora survey priority.

Araracuara Fern. Alonso, a new genus of Rhamnaceae only known from the sandstone plateaus of the Colombian Amazon, is described and illustrated. Its possible affinities are discussed and it is proposed that this is a relictual genus related to the pantropical Colubrina and to a lesser degree with the Amazonian Ampelozizyphus. Also included are both a key to the Colombian genera of Rhamnaceae and a list of representative specimens of the genera studied (some of which have been poorly documented in Colombia).