GENETIC STRUCTURE OF THE AUSTRALIAN CYCAD, MACROZAMIA COMMUNIS (ZAMIACEAE)'

Cycads have been the subject of a wide variety of botanical studies. However, nothing is known of the genetic structure of their populations. Seeds were collected from five populations of the common Australian cycad Macrozamia communis along a north to south transect through its 500-km-long range in eastern New South Wales. Leaf samples from seedlings grown from those seeds were the subject of isozyme analysis. Nine of the 18 isozyme loci studied were polymorphic. Levels of polymorphism varied among loci and among populations. The three southern-most populations were genetically similar to one another but well differentiated from the other two. The levels of species-wide genetic diversity observed for M. communis were relatively low compared with those of other gymnosperms and angiosperms. On the other hand, the levels of spatial differentiation were relatively high, especially compared with other gymnosperms. THE CYCADS (Cycadaceae, Stangeriaceae, Zamiaceae, Boweniaceae; Johnson, 1959; Stevenson, 1985) are a group of gymnosperms with a fossil record extending back to the Lower Permian (Crane, 1988). Relationships among the ten extant genera are obscure, and the group retains a number of primitive morphological, anatomical, and reproductive traits (Sporne, 1974; Deghan and Deghan, 1988). Despite the overall conservative morphological and ana