Molecular systematics of Australian Podolepis (Asteraceae: Gnaphalieae): evidence from DNA sequences of the nuclear ITS region and the chloroplast matK gene

Abstract

The generic circumscription and intra-generic relationships of the genus Podolepis Labill., with various chromosome numbers from n = 12 to n = 3, were examined by sequences of the internal transcribed spacers (ITS) of nuclear ribosomal DNA and the matK gene of chloroplast DNA. The topology of the ITS tree for 17 species and the matK tree for 18 species of the genus Podolepis sensu Davis (1957) and Anderberg (1991) and 15 taxa from eight related genera (Anderberg 1989, 1991, 1994) are basically concordant. Except for P. georgei Diels andP. kendallii F.Muell., parsimony analyses support the monophyly of the genus Podolepis sensu Davis (1957) and Anderberg (1991). The genera of Asteridea Lindl. and Pterochaeta Steetz are sisters toPodolepis in the combined tree based on the ITS and matK sequences. Within the monophyletic clade of the genus Podolepis, three lineages are identified. The chromosome base number of x = 12 may be ancestral in the genus Podolepis. The dysploidal reduction in chromosome number from n = 12 to n = 10 and 9, from n = 12 to n = 8 and 7, and from n = 12 to n = 11 and 3 in three lineages, respectively, is the primary mode of chromosomal evolution in this genus. Total karyotypic length (= genome size) is much greater in perennials than in annuals within the genus Podolepis. The number of pappus bristles on outer female florets tends to decrease and they are absent in some annuals of this genus, while myxogenic cells on the pericarp become prominent.