On the basis of pollen morphology and floral characters, Ipomoea caloxantha is transferred to Merremia. While revising the Convolvulaceae for the Flora ofChina, the name Ipomoea caloxantha Diels came to our attention. Fang & Huang (1979) listed I. caloxantha at the end of their treatment for Ipomoea with a Chinese translation of Diels's original description, but did not include it in their key to species of the genus nor give it any further discussion. Based on Diels's description of the corolla as "intense lutea" and "flowers bright yellow," one of us (GWS) suspected this to be a Merremia, in which genus yellow corollas are fairly common, whereas very few Ipomoea species have them. The holotype of I. caloxantha was examined, and the suspicion proved correct. A quick check of the pollen grains under the dissecting microscope showed them to be nonspinulose, more or less spherical, and apparently 12-rugate. This conforms to Type 3 pollen described for Merremia in the terminology of Ferguson et al. (1977). A new combination is therefore necessary. Merremia caloxantha (Diels) Staples & R. C. Fang, comb. nov. Basionym: Ipomoea caloxantha Diels, Notes Roy. Bot. Gard. Edinburgh 5: 203. 1912. TYPE: China. Yunnan (western): valley of the Mekong, at the crossing of the Teng-Yueh-Talifu road, lat. 25?18'N, 4200 ft., Sep. 1903, G. Forrest 1111 (holotype, E). An amplified description of Merremia caloxantha will be published in the Flora ofChina. We maintain this species until further study can be devoted to Merremia in Asia, where the species are inadequately known, at best, and it is quite possible that other species remain to be described, or may have already been described under Ipomoea. Acknowledgments. We thank the Keeper of the Herbarium at the Royal Botanic Garden, Edinburgh, for the loan of the holotype and Ihsan Al-Shehbaz for expediting the publication of this brief note.