Taxonomy, cytology and ecology of indigenous Australian sorghums (Sorghum Moench: Andropogoneae: Poaceae)

Abstract

The indigenous component in Australian sorghums comprises 17 species and 1 variety of which 14 species and the variety are endemic, and 8 taxa are new. Sorghum brevicallosum is reduced to a synonym of S. timorense, which also includes S. australiense. Four previously established, subgenera are accepted with modified circumscriptions and floristic compositions. On morphological evidence, subgenus Stiposorghum represents the most advanced members and subgenus Para-Sorghum the most primitive. Some taxa are polymorphic; others exhibit unique features. Characters relating to pubescence, pruinosity, nervation, lodicules and caryopsis are considered to be unspecialised. First chromosome counts are recorded for eight species. Polyploidy characterises the indigenous species, which comprise diploids, tetraploids, hexaploids and octaploids. Ploidy levels are consistent within the majority of species, but vary in some. The chromosomes of S. macrospermum are markedly smaller than those of any other indigenous species. Cleistogamy occurs in S. laxiflorum. Some species are habitat-specific; many are widely adaptable. With few exceptions, the annual species have restricted distributions. Ecological aspects discussed include seed dormancy and germination, the effects of fire, and patterns of vegetative and floral development phases. Nutritionally, the herbage of both annual and perennial species is deficient in macronutrients, and lacks sufficient N and P to maintain beef cattle. Only the seedheads of S. macrospermum have similar N and P concentrations to those in the grain of the cereal S. bicolor, and in the past they were an important source of starchy food for Aborigines. All the indigenous taxa constitute a genetic resource for potential utilisation by plant breeders.