Pollen Morphology of Three Selected Species from Annonaceae

Dry pollen grains of Asimina longifolia var. spatulata, A. reticulata, and Disepalum plagioneurum were described based on scanning electron microscopy to provide evidence for phylogenetic analysis. Results showed that most pollen grains were tetrads. Occasionally,dyads and triads were found in A. reticulata,and polyads were also observed in D. plagioneurum. Most of the tetrads were rhomboidal tetrads,though tetragonal tetrads were also observed in A. reticulata and D. plagioneurum. The ornamentations of the pollen walls were regulate (A. longifolia var. spatulata),microreticulate (A. reticulata) or reticulate (D. plagioneurum). Pollen grains of neighboring tetrads were connected by either short exine connections or pollen-connecting threads. The function of the cohesion among tetrads was to enhance pollination efficiency by enabling fertilization of multiple ovules in a single pollinator visit. Wall ornamentation and tetrad pollen grains in Asimina were similar with those of Disepalum,which supports their close phylogenetic relationship.