Vicariance biogeography and terrane tectonics in the South Pacific: analysis of the genus Abrotanella (Compositae)

Abstract

The species of Abrotanella (Compositae) form mats and cushions a few centimetres high and up to a metre or more in diameter. The flowers are less complex than those of most Compositae and lack a pappus, the usual means of dispersal in the family. There are 20 species, all restricted to mountains of Australasia and southern South America. The putative affinities of Abrotanella involve several tribes of Compositae and the genus is not considered derived within the family. A comparative analysis of areas of endemism in Abrotanella shows clear patterns of vicariance and disjunction shared with many plants and animals, and long-distance dispersal is rejected as an explanation. Abrotanella and the three genera related to it are all restricted to lands bordering the Pacific. Areas previously accepted as areas of endemism, such as New Guinea, Tasmania, New Zealand and southern South America, are shown to be polyphyletic complexes, rather than simple areas. Use of such areas in area cladograms leads to the erroneous interpretation of taxa-area relations as incongruent. Distributions of the taxa in Abrotanella are correlated with tectonic features such as plate margins, transform faults and fracture zones, and processes such as continental rifting, terrane accretion, granite emplacement and orogeny. Abrotanella patearoa sp. nov., a high-alpine cushion-plant, is described from mountains of eastern Central Otago: Rock and Pillar Range, Lammerlaw Range, Umbrella Mountains and Garvie Mountains. (C) 1999 The Linnean Society of London.