Sporobolus virginicus (L.) Kunth in Coastal Australia: the Reproductive Behaviour and the Distribution of Morphological Types and Chromosome Races

Abstract

Sporobolus virginicus (L.) Kunth is essentially a littoral grass distributed over much of the coastline of Australia. It occupies a number of different habitats, and exists as morphologically distinct variants and chromosomally distinct races. Four morphological forms are here recognised (designated types 1-4) that do not conform to currently defined subspecific taxa. Cytological investigation of somatic cells has determined six different chromosome numbers: 2n = 20, 30, 3 1, 40, 50 and 60. The counts of 2n = 31, 50 and 60 are the first records of these numbers for the species.

Races, defined by morphological type and chromosome number, were found to be discretely distrib- uted, with diploid populations (2n = 20) occurring only in the southern regions and polyploid popu- lations predominantly (but not solely) in the northern half of the continent. This pattern is presumed to reflect a high level of local evolution, with substantial physiological adaptation to climatic and ecological conditions.

Whilst all races were found to reproduce asexually, by way of stolons and rhizomes, instances of sexual reproduction were recorded only from the diploid and tetraploid cytotypes. Possible subsexual reproduction by way of agamospermy was observed in the triploid race and also in one diploid plant and inflorescence proliferation was found to be a feature of one pentaploid clone.