Phylogenetic analysis and generic limits of the tribe Pomaderreae (Rhamnaceae) using internal transcribed spacer DNA sequences

Abstract

The tribe Pomaderreae (Rhamnaceae) currently consists of approximately 180 species in seven genera, endemic to Australia and New Zealand. It is the second largest tribe of Rhamnaceae. We undertook a phylogenetic analysis using internal transcribed spacer (ITS) sequence data from 69 representative species of Pomaderreae and five outgroup taxa. The monophyly of Pomaderreae was confirmed. The clades found in the strict consensus tree are mostly consistent with the currently accepted genera of the tribe. All major clades, except Stenanthemum, received moderate to strong bootstrap and jackknife support. Only the relationship between Siegfriedia and Pomaderris received strong support; relationships between other genera did not receive support above 50%. Taxonomic changes are suggested and a preliminary classification of Pomaderreae is proposed, including the monophyletic genera Cryptandra, Pomaderris, Spyridium and Trymalium. Blackallia and Siegfriedia are monotypic. Two new genera are required: one containing two atypical species of Stenanthemum and the second genus consisting of previously unrelated species from three genera that share a 2-carpellate ovary and a characteristic indumentum. The taxonomic status of Stenanthemum requires further examination. A split of Cryptandra into smaller genera is not supported.