Fruit features in relation to the ecology and distribution of Acaena (Rosaceae) species in New Zealand

Fruit features of 17 Acaena species in New Zealand were investigated to determine the relations between reproductive allocation patterns, mode of dispersal and species ecology. Three basic morphological types, corresponding to major sections within the genus, are represented: spineless fruits (Sect. Pteracaena—one species), spined fruits lacking barbs (Sect. Microphyllae—6 species), and spined fruits with barbs (Sect. Ancistrum—10 species). The presence of terminal barbs on spines enhances fruit adhesion to animals, and is associated with the development of longer scapes, globular many-fruited capitula, and smaller single-seeded fruits. Barb-spined species generally have the broadest geographical range and habitat distribution within New Zealand, and are the only species of Acaena to occur in forests or on offshore islands. These species are generally strongly stoloniferous. Acaena species with barbless spines and/or no spines are often regional endemics confined to open and/or localised habitats, are rhizomatous, and may be dispersed by water, ingestion or wind. There is a tight correlation between intrageneric classification and species ecology and fruit features which requires testing via independent phylogenetic analysis based on molecular genetic characters. Although avian dispersers have declined since human settlement, introduced mammals may be performing a similar function for barbed Acaena species.