The reproductive biology of the early-divergent genus Anaxagorea (Annonaceae), and its significance for the evolutionary development of the family

摘要

Data of six studied Neotropical Anaxagorea species are analyzed and discussed with respect to the population structure, flowering phenology, flower morphology, anthesis, scent emission, thermogenesis, floral visitors, breeding system, fruit-set and seed dispersal. The probably reason for the patchy distribution of small populations of Anaxagorea species within lowland tropical forests is given. A novel explanation of the functional significance of ruminate endosperm is presented. Flowering of the species follows either the annual or the continuous flowering pattern. All studied species have diurnal, two-day lasting, protogynous anthesis; several species have thermogenic flowers. Self-compatibility appears to be the prevailing reproductive system in the genus. However, there is a strong tendency for effecting cross-pollination. Floral scent of Anaxagorea species contains fruit-like components, and the pollinators, primarily Nitidulidae (Colopterus spp.) are attracted by deceit. Strong scenting pollination chambers occur also in most other cantharophilous Annonaceae. Novel floral developments are apparent mainly in fly-, cockroach- and bee-pollinated Annonaceae, which have patterns different from cantharophilous species and exhibit open flowers with reflexed petals, which allow their pollinators to reach and touch the reproductive organs.