Systematics and ecology of the Australasian genus Empodisma (Restionaceae) and description of a new species from peatlands in northern New Zealand

Abstract

The genus Empodisma comprises two species that are ecologically important in wetland habitats. Empodismagracillimum is restricted to south-western Australia, whereas E.minus is found in Tasmania, eastern Australia and New Zealand. We sequenced three cpDNA genes for 15 individuals of Empodisma sampled from throughout the range of the species. The results support an Australian origin for Empodisma sometime during the late Oligocene to early Miocene with more recent dispersal, colonization and diversification in New Zealand. We recovered six genetically distinct maternal lineages: three E. gracillimum haplotypes corresponding to the three accessions in our analysis, a wide-ranging E. minus haplotype found in eastern Australia and Tasmania, an E. minus haplotype found in New Zealand from Stewart Island to approximately 38° S latitude on the North Island, and a distinct haplotype restricted to the North Island of New Zealand north of 38° S latitude. The Eastern Australian and New Zealand haplotypes of E. minus were supported by only one cpDNA gene, and we felt the relatively minor morphological differences and the small amount of genetic divergence did not warrant taxonomic recognition. However, we recommend that the northern New Zealand haplotype should be recognized as the new species Empodisma robustum and provide descriptions and a key to the species of Empodisma. Monophyly of E. robustum is supported by all three cpDNA genes. Empodisma robustum can be distinguished from E. gracillimum and E.minus by its robust growth stature and distinct ecology. It is typically eliminated by fire and re-establishes by seed (seeder strategy), whereas E.minus and E. gracillimum regrow after fire (sprouter strategy).