Distribution and cytology of Australian Neurachne and its allies (Poaceae), a group containing C₃, C₄ and C₃-C₄ Intermediate species

Abstract

Cytological, phytogeographical and habitat data are presented for the Neurachneae (Poaceae), a tribe endemic to Australia and containing seven C₃ two C₄ and one C₃-C₄ intermediate species. Chromosome counts for 34 accessions Australia-wide reveal a typical eu-panicoid base number (x = 9). Three species are diploid (Neurachne tenuifolia C₃, Thyridolepis mitchelliana C₃ and T. xerophila C₃,); four species (Paraneurachne muelleri C₄, N. minor C₃-C₄, N. lanigera C₃, T. multiculmis C₃) are tetraploid only, one (N. queenslandica C₃) is hexaploid only, while two (N. alopecuroidea C₃ and N. munroi C₄) are variable. Aneuploidy was found in individuals of N. minor (2n = 4x+1) and N. queenslandica (2n = 6x -1). Chromosomes are small (mean c. 2 µm) and metacentric or submetacentric. Using localities derived from all known collections in Australian herbaria, actual and computer-predicted distributions were mapped using the Bioclimate Prediction System (BIOCLIM) developed by H. A. Nix and J. R. Busby. Species distributions, habitats and chromosome counts are discussed in relation to photosynthetic pathway, present and past climates and evolutionary history. The Neurachneae are mainly subtropical, arid and semiarid zone plants. However, the distribution of their C₃ species contrasts with those of other C₃ eu-panicoids and C₃ grasses as a whole. The temperate species N. alopecuroidea is the only native C₃ eu-panicoid known from south-western Australia. It is suggested that phenotypic expression of C₄, photosynthesis in the Neurachneae occurred independently of other grasses and that they did not extend into arid and semiarid regions from a mesic temperate zone.