Summary. The genus Girardinia has been found to comprise two species, both restricted to the montane areas in the tropics and in the warmer temperate parts of the Old World: G. bullosa is a well defined species restricted to Ethiopia and East Africa; G. diversifolia is a polymorphic species distributed from West Africa to China, Korea, Taiwan and Indonesia. G. cuspidata is found to be a Laportea, and the necessary new combination is made. In connection with my study of African Urticaceae for the Flora of Tropical East Africa it has been necessary to study the genus Girardinia in some detail. It has long been considered difficult to name specimens of this genus with any degree of certainty, but the latest account of the genus (Letouzey 1968) suggested that only two species existed in Africa: the East African G. bullosa, and G. heterophylla, a very widespread species which occurred from West Africa through tropical Africa, Arabia and India to China and Mainland SE Asia. It appeared, however, from the synonymy given for G. heterophylla by Letouzey that the name for this species was illegitimate, and that some other epithet, probably from an Asian taxon, would have to be used instead. A study of the whole genus seemed inevitable in order to solve this problem, and material from the following herbaria was obtained on loan: A, AAU, B, BM, BR, C, CAL, COI, E, FI, G, K, L, LE, LISC, LISU, MH, MO, P, PDA, SING, TAIF, UPS, W, WU. The genus seems to be avoided by collectors because of the fiercely stinging hairs, and the total amount of material preserved in herbaria is comparatively scarce in view of the wide distribution. A total of c. 400 collections have been seen. The study confirmed the basic findings of Letouzey, but it was also found that all hitherto described species of Girardinia, with the exception of the above mentioned G. bullosa and two species which had to be excluded from the genus, were in fact connected by intermediate forms. The only satisfactory solution to this taxonomic problem was to merge all these species into one and, in fact, species with such a wide range of distribution are well known from the Urticaceae. Laportea interrupta (L.) Chew, Laportea aestuans (L.) Chew, Boehmeria platyphylla D. Don, and Parietaria debilis G. Forster are examples of species with an equally wide distribution, and the latter three species are almost as polymorphic. The nomenclature was found to be quite complicated, with a long range of illegitimate names, and it seems inevitable that a new combination based on the oldest available epithet, Urtica diversifolia, has to be made. More detailed notes on nomenclature and taxonomy of this species are given below.