Biology of the salinity tolerant genus Ruppia L. in saline lakes in South Australia I. Morphological variation within and between species and ecophysiology

Abstract

Wide variations in salinity, water depth and water permanence limit the distribution and diversity of plant communities in a range of saline ecosystems in the south-east of South Australia. Once water salinity exceeds 4% TDS the macrophytes are restricted to species of two genera of angiosperms, Ruppia L. and Lepilaena Drumm. ex Harvey and a few species of algae. Species of Ruppia were the focus of studies on the adaptations of plants in unpredictable environments. Two growth forms of Ruppia, distinctive in life history and habitat occur. R. polycarpa Mason and R. tuberosa Davis and Tomlinson are both small delicate annuals which occur most commonly in temporary (but occasionally in permanent) waters 0.1–0.4 m deep with salinities up to 230% TDS. R. megacarpa Mason is a large (up to 2.5 m) robust perennial which occurs only in permanent waters up to 3 m deep with salinities between 12 and 50% TDS. R. megacarpa plants persist in permanent waters whereas R. tuberosa and R. polycarpa plants survive drying and desiccation as seeds or perennating organs in temporary habitats. Taxonomic and ecological investigations of the annual and perennial forms revealed both species differences and phenotypic variation within species. Comparative studies of the reproductive biology, life history and physiological requirements and tolerances emphasized the distinctions between the two life forms in relation to their habitats. The morphological variation and aspects of the ecophysiology of the genus are reported in this paper. The population biology and reproductive biology are reported in the following paper.