MOLECULAR PHYLOGENETICS OF CALYCADENIA (COMPOSITAE) BASED ON ITS SEQUENCES OF NUCLEAR RIBOSOMAL DNA - CHROMOSOMAL AND MORPHOLOGICAL EVOLUTION REEXAMINED

Phylogenetic patterns within Calycadenia were estimated from 18-26S nuclear ribosomal DNA sequences of the internal transcribed spacer (ITS) region in 19 representatives of all species in Calycadenia, including Osmadenia (C) tenella, and in two outgroup species. In pairwise comparisons among the Calycadenia and Osmadenia sequences, divergence ranged from 0 to 11.2% of nucleotides in ITS 1 and from 0 to 8.6% in ITS 2. Of 62 nucleotide sites with potential phylogenetic information, 51.6% were in ITS 1, 46.8% were in ITS 2, and 1.6% were in the 5.8S subunit. A highly resolved, strict consensus tree from Wagner parsimony analysis of these data agrees well with morphological and cytological evidence. This tree suggests that: t) the monotypic Osmadenia tenella is the sister-group to Calycadenia; 2) the base chromosome number in Calycadenia is n = 7, from which other numbers were derived; 3) species with multiple T-glands on cylindrical bracts and chromosome numbers of n = 5 or 6 (or 7 in C oppositifolia) form a monophyletic group derived from an n = 7 species similar or identical in genomic structure to C. hooveri or C villosa; 4) C. spicata (n = 4) is the product of an independent dysploid reduction from n = 7; 5) C multiglandulosa and C. pauciflora, sensu Keck, are not monophyletic taxa; and 6) loss of chromosomal homology between Calycadenia species, as reflected by meiotic chromosomal association in hybrids, is positively correlated with time since evolutionary divergence. These results offer little evidence of homoplasy in chromosomal and phenotypic characters in Calycadenia and provide further support for the phylogenetic utility of plant ITS sequences.