Ecology of Chondrilla Juncea L. in South-Eastern Australia

Chondrilla juncea, an apomictic Composite of Eurasian steppe origin and with considerable powers of vegetative reproduction from root buds, appeared in south-eastern Australia in 1917 and now occupies most of the wheat belt of the continent. The regional climatic limits of the species appear to be set by the high summer temperature requirement for flowering and seed formation coupled with a nicely balanced rainfall distribution which will satisfy the need for adequate soil moisture for seed setting without bringing about mass seed germination until the onset of lower autumn temperatures. The local distribution pattern is determined by soil texture, availability of soil calcium and phosphorus, and the occurrence of open plant communities where root competition and shade effects are minimal. The species thus finds its optimum in cool winter/warm summer climates without severe summer drought, but with a distinct rainfall `break' in autumn, on light-textured soils of moderate to high calcium and phosphorus status but with limited supplies of available nitrogen to limit the luxuriance of competitors. It is thus perfectly adapted to a cereal-fallow system of agriculture in which superphosphate fertilizer is freely used.