Aust. J. Bot., 1991, 39, 487-96 Vegetative Variation of Myriophyllum variifolium in Permanent and Temporary Wetlands Margaret A. Brock and Michelle T. Casanova Department of Botany, University of New England, Armidale, N.S.W. 2351, Australia. Abstract The responses of vegetative fragments of Myriophyhm variifolium J. Hooker to environmental variation in a field transplant trial are reported. Plant performance was measured as survival of plants, number of shoots and shoot length per surviving plant. Vegetative fragments from several lakes and different habitats within lakes were grown at three depths, in two regimes of disturbance by grazers and in two soils. The effect of depth was marked. Plants established and survived best on the shore (0-m depth) where their growth form was dominated by many shoots and prostrate spread. In contrast, plants in deeper water had low survival rates and surviving plants had single or few upright shoots. Separate analysis of the shore results indicated significant differences in plant performance between plants of various origin, between soil types and between regimes of disturbance by grazers. Plants originating from the deep water habitat consistently performed poorly whereas plants originating from the shore of the transplant site survived and grew well. Soil type had a major effect in the establishment phase of plant growth. Plants performed better on permanently wet basaltic soils (taken from the experimental transplant site) than on granitic soils from a temporary lagoon. The presence of grazing animals encouraged greater numbers and lengths of shoots on the shore. The role of flexibility in plant performance and vegetative reproduction in maintaining plant pop- ulations in lakes with unpredictable fluctuations of environmental conditions is discussed. Introduction Myriophyllum variifolium J. Hooker is an aquatic plant which grows in a wide range of permanent and temporary fresh waters in eastern Australia. Orchard (1985) reported it as an obligate aquatic and on the northern tableland of N.S.W. it does grow in permanent water to 1.5 m; however, it also grows stranded out of water when wetlands become temporary (Brock 1988; Brock 1991). The species occurs in a variety of growth forms, habitats and community dominance in a wide range of ecologically different wetlands. We therefore chose it for observation and experimentation in an attempt to discover how one species copes with widely fluctuating environmental conditions. Knowledge of the behaviour of individual species may help us to predict the biological consequences of environmental change. The use of transplant studies to examine the importance of natural selection in the adaptation of local populations to their environments is emphasised by Primack and Kang (1989). Terrestrial and salt marsh species' responses in field transplant trials have been reported (e.g. Harper 1977; Schmidt and Levins 1985; Davy and Smith 1988) but comparative studies of plants in aquatic or amphibious habitats are sparse (Crawford 1987). Crawford's (1989) synthesis of studies on plant adaptation to adversity did not consider environmental fluctuations in aquatic systems. The response of Australian aquatic plants to environmental changes in wetlands 0067-1924/91/050487$05.00