The distribution of C and C grasses in Australia in relation to climate.

All but four of 833 native and 292 naturalised Australian grasses (Poaceae) have been assigned as having the C or C photosynthetic pathway. In conjunction with comprehensive species composition data for 75 geographic subdivisions Australiawide, this has permitted the construction of distribution maps for C and C grasses. C and C grass distributions have been considered (i) independently, using subdivisional native species numbers; and (ii) relatively, using 'subdivisional % C'. C species are most numerous in the Southern Tablelands (New South Wales), the QZ subdivision (Victoria), and Tasmania; C species in the northern Northern Territory and northern Queensland, including the Cook subdivision where 54% of Australia's native C grasses can be found. C species predominate only in south-west Western Australia, parts of southern South Australia, the Tablelands, central and south coast, and south western slopes of New South Wales, Victoria and Tasmania. C species predominate over 80-85% of the continental area. For 16 temperature and rainfall variables, subdivisional area-weighted means were calculated, and correlation analyses performed. C species number correlates most highly with January average maximum temperature (-ve) and spring rainfall (+ve); C species number with October average minimum temperature (+ve) and February median rainfall (+ve); '%C' with January average minimum temperature (+ve). Predictive multiple linear regression equations were generated using climatic variables. In general, C grass species, like C species, increase in number with increasing rainfall, in their preferred temperature regime. C species are most numerous where the summer is hot and wet; C species where the spring is cool and wet. C species numbers decline with decreasing temperature and/or decreasing summer rainfall; C species numbers decline with increasing temperature and/or decreasing spring rainfall. Results are also considered in relation to the taxonomic and physiological heterogeneity of grasses and to Australia's geobotanic history.