Pollination biology of basal angiosperms (ANITA Grade)
Abstract
The fi rst three branches of the angiosperm phylogenetic tree consist of eight families with ~201 species of plants (the ANITA grade). The oldest fl ower fossil for the group is dated to the Early Cretaceous (115 – 125 Mya) and identifi ed to the Nymphaeales. The fl owers of extant plants in the ANITA grade are small, and pollen is the edible reward (rarely nectar or starch bodies). Unlike many gymnosperms that secrete “ pollination drops, ” ANITA-grade members examined thus far have a dry-type stigma. Copious secretions of stigmatic fl uid are restricted to the Nymphaeales, but this is not nectar. Floral odors, fl oral thermogenesis (a resource), and colored tepals attract insects in deceit-based pollination syndromes throughout the fi rst three branches of the phylogenetic tree. Self-incompatibility and an extragynoecial compitum occur in some species in the Austrobaileyales. Flies are primary pollinators in six families (10 genera). Beetles are pollinators in fi ve families varying in importance as primary (exclusive) to secondary vectors of pollen. Bees are major pollinators only in the Nymphaeaceae. It is hypothesized that large fl owers in Nymphaeaceae are the result of the interaction of heat, fl oral odors, and colored tepals to trap insects to increase fi tness.