Morphology and adaptation of aquatic mosses in an Antarctic lake

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Abstract
Two species of moss growing in Moss Lake on Signy Island, South Orkney Islands, had unusual morphologies with large leaves and long internodes. Both Calliergon sarmentosum and Drepanocladus cf. aduncus differed from their terrestrial counterparts and from each other in their leaf characteristics. The 2 genera differed in the ability of the terrestrial forms to develop a large-leaved growth form. Calliergon, which was represented by the same species in both environments, changed to the aquatic morphology when separated shoots were grown either submerged or under damp conditions. Light intensity was not an important factor influencing change in morphology. The terrestrial D. uncinatus, the closest taxonomic counterpart of D. cf. aduncus on Signy Island, did not show any adaptation under similar conditions. The aquatic forms showed a corresponding degree of plasticity in their natural habitat. Calliergon varied from robust shoots to microphyllous or even leafless stems whereas D. cf. aduncus only grew in the robust form. These differences were related to the success of the 2 spp. at different depths and the very low compensation points of the 2 mosses apparently resulted from the morphology of the plants.