Convergent evolution and adaptive radiation of beetle-pollinated angiosperms

A literature review of 34 families of flowering plants containing at least one species pollinated primarily by beetles is presented. While the majorit y of species are represented by magnoliids and basal monocotyledons special ized, beetle-pollinated systems have evolved independently in 14 families o f eudicotyldons and six families of petaloid monocots. Four, overlapping mo des of floral presentation in plants pollinated exclusively by beetles (Bil abiate, Brush, Chamber Blossom and Painted Bowl) are described. Chamber Blo ssoms and Painted Bowls are the two most common modes. Chamber Blossoms, fo und in magnoliids, primitive monocotyledons and in some families of woody e udicots, exploit the greatest diversity of beetle pollinators. Painted Bowl s are restricted to petaloid monocots and a few families of eudicots depend ent primarily on hairy species of Scarabaeidae as pollen vectors. In contra st, generalist flowers pollinated by a combination of beetles and other ani mals are recorded in 22 families. Generalist systems are more likely to sec rete nectar and exploit four beetle families absent in specialist flowers. Centers of diversity for species with specialized, beetle-pollinated system s are distributed through the wet tropics (centers for Brush and Chamber Bl ossoms) to warm temperate-Mediterranean zones (centers for Painted Bowls an d a few Bilabiate flowers). It is unlikely that beetles were the first poll inators of angiosperms but specialized, beetle-pollinated flowers must have evolved by the mid-late Cretaceous to join pre-existing guilds of beetle-p ollinated gymnosperms. The floras of Australia and western North America su ggest that mutualistic interactions between beetles and flowers has been a continuous and labile trend in angiosperms with novel interactions evolving through the Tertiary.