The systematics and historical biogeography of the asteliaceae (asparagales)

Abstract

The flowering plant family Asteliaceae (Asparagales) contains four genera and approximately 36 species. The family has a center of diversity in New Zealand and a distribution spanning Austral and Pacific regions. Evolutionary relationships within the family were inferred based on phylogenetic analyses of molecular (chloroplast and nuclear) and morphological (vegetative, reproductive and cytotaxonomic) data representing 35 of the 36 Asteliaceae species. Congruent phylogenies were obtained from analyses of the molecular and the combined molecular and morphological datasets. The monophyly of the Asteliaceae cannot be determined based on these data as the relationships of the Lanariaceae, a closely related family in the astelioid clade, are unresolved. A broadly circumscribed Astelia s.l., including Collospermum, is recognized to achieve monophyly of this genus. Synapomorphic characters for Astelia s.l. include its dioecious or polygamodioecious gender allocation, pistillate flowers with a 3-lobed stigma, and fleshy unilocular or trilocular fruit. Astelia subgenera Astelia and Asteliopsis are polyphyletic and subgenus Tricella is paraphyletic. Section Tricella is also paraphyletic. However, Astelia sections Asteliella, Desmoneuron, Isoneuron, Micrastelia, Palaeastelia, and Periastelia are monophyletic. Revised taxonomic hypotheses are proposed for Astelia s.l. subgenera. These include subg. Astelia excluding sect. Desmoneuron, subg. Asteliopsis including sect. Desmoneuron and excluding sect. Periastelia, and subg. Tricella including sect. Periastelia. Taxonomic revision of Astelia s.l. is necessary. The Asteliaceae phylogeny provided the basis for the estimation of divergence dates and ancestral areas to infer the biogeographic history of the Asteliaceae. The Asteliaceae crown group radiated at ca. 59.5 Ma; that is, during the Late Palaeocene. An Australian origin for the Asteliaceae is proposed, although subsequent radiation of Astelia s.l. occurred elsewhere, primarily in New Zealand. Astelia s.l. is the oldest genus in the family with the crown group radiating in Australia or New Zealand at ca. 40.0 Ma, thus during the Late Eocene to Early Oligocene. Neither evolutionary relationships nor divergence date estimates are congruent with results predicted by vicariant scenarios. Rather, results suggest a complex history of long-distance dispersal events for Astelia s.l. including at least three dispersals between Australia and New Zealand and at least four independent dispersals from New Zealand to Pacific islands.