The moss genus Hennediella is taxonomically revised. A key, descriptions, illustrations, distribution data, LM and SEM photographs of the 15 species recognized are provided. A morphometric study of 226 specimens is carried out to test the most significant characters and a multivariate analysis is made for the Hennediella heimii group to distinguish patterns of morphological differentiation. Thirty-seven names are lectotypified and two epitypes designated. Hennediella serrulata and H. angustifolia are transferred to the genus Syntrichia. Desmatodon spelaeus, Hennediella oedipodioides, Pottia chubutensis and Syntrichia astoma are synonymyzed with H. heimii, and Pottia fusco-mucronata and Hennediella acutidentata with H. antarctica. Hennediella acletoi and T. leiostomoides are synonymyzed respectively with H. denticulata and H. longirostris. The sporophyte of Hennediella bellii is described for the first time. New records for various countries of the study area are reported.