Aloe argyrostachys, a remarkable new species described in this paper, is related to A. compressa H. Perrier (s.l.) from which it differs, inter alia, by its caulescent habit and larger size and by its white perianths, with segments not recurved, held in a dense, conical raceme. The species was found in the wide expanse of quartzite mountains that constitute much of the country west of Antsirabe, in the central highlands of Madagascar.