Analyzes on adaptive radiation of semi-desert Asteraceae.

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We have collected 550 population samples of Australian Astereae and Gnaphalieae and investigated their habitat conditions by two field expeditions.Chromosome numbers from 200 populations attributed 100 species of nine genera of Astereae were determined. The frequent dysploidy has been found in the genera of Brachyscome and Calotis. Species of arid regions frequenthy display an annual habit and have the complex structures of fruit, such as wings, inflated spongy projections and silky long hairs served as the effective seed dispersal, and these are correlated with lower chromosome numbers. Chromosome numbers from 50 species of 23 genera of Gnaphalieae were determined. Although the chromosome base number of Gnaphalieae outside of Australia is constant on x=7, the variable dysploidy series in Podolepes (n=12-3), Pogonolepis (n=6-4), Rhodanthe (n=11-5) and Tricanthodium (n=4-3) were found. To clarify the species relationship and the evlolutionary trends in chromosome number, habit and morphological characters, we have compared the pattern of RFLP and the nucleotide sequence of mat K gene of chlorplast between species and constructed the molecular phylogenetic trees of Brachyscome. Both trees are consistent and support the monophyly of this genus. They also inditate that Brahcyscome is divided into 4 clusters corresponding to the morphology of anther appendage and style, geographical distribution and the variation pattern of chromosome number. The dysploid reductions from n=9, the change of habit from perennial to annual and the change of fruit morphology from simple to complex have been derived in parallel of several lineages and these derived characters are regarded to be adaptive under the arid or seasonally dry conditions.