Morphological, evolutionary and taxonomic aspects of Australian and New Zealand Microseris (Asteraceae)

The Australian and New Zealand Microseris is supposed to have evolved from one or a few diaspores after a unique event of long-distance dispersal from western North America. At present, the plant group includes two species, M. lanceolata (Walp.) Sch.-Bip. and M. scapigera (Forst.) Sch.-Bip., each with two morphologically and ecologically divergent ecotypes. In spite of this classification, the morphological variation within and among ecotypes is not entirely consistent, and molecular investigations show evidence for the, possibly recent, occurrence of hybridisations between plants of different ecotypes. The present study investigates the overall morphological similarities among 1-4 plants of each of 54 Australian and New Zealand Microseris populations. The aim of the study was to gain further insights into the delimitation of species and ecotypes, the placement of populations that could thus far not be assigned to an ecotype and the adaptive radiation of the plant group. The results confirm the previously defined ecotypes and assign all but two of the questionable populations to ecotypes. They show that a broad range of character states rather than a few 'diagnostic' ones are specific for the ecotypes. The data confirm our earlier conclusion from molecular results, indicating that ecotype characteristics are maintained or re-established by selection or adaptation, after dispersal or hybridisation between ecotypes. Despite (incidental) genetic exchange among populations of different ecotypes, the process of adaptive radiation is progressing. The combined morphological and molecular results are not incongruent with the present species delimitation. However, they also may support the split up of M. scapigera into two species and other phylogenetic solutions.