Intra-specific differences in desiccation injury are shown in collections of Acrocladium cuspidatum, Climacium dendroides and Hypnum cupressiforme from habitats subjected to a wide range of moisture stresses. The degree of desiccation tolerance is correlated with degree of moisture stress in the habitat. Desiccation injury was measured as the decline in the initial rate of photosynthesis on remoistening. Collections of species from habitats in which severe moisture deficits occur show a slower decline in photosynthesis on desiccation and a more rapid recovery of function on wetting than collections from habitats with no appreciable moisture deficits. The results are discussed in terms of their ecological and physiological significance.