SYSTEMATICS OF AUSTRALIAN LEPIDIUM SPECIES (BRASSICACEAE) AND IMPLICATIONS FOR THEIR ORIGIN - EVIDENCE FROM IEF ANALYSIS OF RUBISCO

Abstract

Variation in subunit polypeptide composition of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from native Australian Lepidium taxa was analyzed by isoelectric focusing (IEF). Species of grex Monoplocoidea on the one hand, and species of greges Pseudoruderalia and Papillosa on the other, were well separated by Rubisco IEF patterns. The protein data suggest grex Monoplocoidea to be placed in sect. Monoploca whereas greges Pseudoruderalia and Papillosa should be integrated into sect. Dileptium. We suggest that the Rubisco type of American and/or Asian Lepidium species was contained in those plants migrating to Australia and evolving into the recent native Australian species. Fossil pollen records and vegetation history indicate that the origin of Lepidium in Australia was restricted to the late Tertiary of Quaternary. Data presented in this study fit best with an immigration by long-distance dispersal of seeds by birds from Asia and/or from South America.