We have suggested1 that Antarctic lakes offer a more favourable physical environment to certain species of moss than the surrounding land. We now present evidence in support of the wider thesis that in certain areas of Antarctica most of the plant biomass occurs in aquatic habitats. In the austral summer 1973–74 we found more mosses and algae growing aquatically than terrestrially in the Ablation Valley area of Alexander Island (Fig. 1). The area is relatively free from ice and has a climate similar to the inland ice-free areas of continental Antarctica2, although conditions are not quite so arid because of frequent intrusions of oceanic weather systems from the Bellinghausen Sea. Extensive terrestrial plant cover was, however, restricted to seven discrete (patches of moss, lichen and algae, totalling 2,300 m2 in about 40km2 of icenfree ground searched on foot. The patches were on north-facing slopes where groundwater welled up continuously during the short summer. Widely scattered, very small moss cushions also occurred between and beneath stones in a few other damp and wet places. The availability of water and soil instability seemed to be the two most important factors restricting terrestrial plant distribution.