The biology and autecology of Nitraria L. in Australia. I. Distribution,morphology and potential utilization

Nitraria billardieri occurs in all mainland states of Australia and on several adjacent islands south of the Tropic of Capricorn between Lat. 25° and 38°S and Long. 113° and 147°E. Other species of Nitraria are found in North Africa, the Middle East and Eurasia. The probability that Nitraria is a very old genus, having its origins in central Asia, is discussed. The wide disjunction between N. billardieri in Australia and the closely related N. schoberi in eastern Europe and Asia is difficult to explain. Observations on various populations grown under nursery conditions at Deniliquin, combined with those undertaken during field traverses across Australia, clearly indicate that considerable inter-population variability occurs. Whether these different forms are ecotypes in which particular characters have become genetically fixed in specific habitats, is uncertain; but the form growing along the Indian Ocean coast of Western Australia shows marked contrasts to the other forms and may ultimately be described as a distinct species. Possible uses for N. billardieri in arid and semi-arid zones of Australia are discussed. Particular reference is made to the abundance of N. billardieri in low shrubland communities which were dominated by chenopods prior to the introduction of domestic livestock. The marked increase in N. billardieri on overgrazed saltbush (Atriplex vesicaria) communities of the Riverine Plain suggests that it may serve as an indicator species in range condition assessment of these communities.