Flowers of angiosperms are the most stable parts among all the organs, thus are the focus of plant taxonomy and systematics, as well as the evo-dev. Even in the molecular era, many taxonomists recognize the plants just by the matural morphological forms of flowers. In fact, different developmental series possess rich taxonomical and evolutionary information. Using Scanning Electronical Microscopy (SEM) benefits us to understand the huge floral diversity and related evolutionary implication.
Dr. Zigang Zhang and Aiping Meng of the Systematic and Evolutionary Group, Wuhan Botanical Garden have an investigation on the floral development of Phyllanthus chekiangensis (Phyllanthaceae) and Stephania (Menispermaceae) this year. The nucellar beak appears as the exposed part of embryonic micropyle. Traditional literatures thought this structure growing and extending beyond the micropyle, and then becoming contiguous with the obturator and contacting pollen tube, finally helping to the completion of fertilization. However, the observation on P. chekiangensis revealed that the nucellar beaks did not grow through the micropyles, and the obturators did not intrude into the micropyles. It probably was the primordial residue of floral apex during the terminant stage.
Generally there are two basic patterns of flower symmetry in the angiosperms: actinomorphy and bisymmetry. The switch between them and related phylogenetic and evolutionary interpretation has long been the important issues. Stephania was the sole genus in the basal eudicot family Menispermaceae that possessed both actinomorphic and zygomorphic flowers. This study revealed that actinomorphy and bisymmetry appear to be two clades. Variation in perianth merism and loss of them in the female flowers may have resulted in the shift of flower symmetry in between actinomorphy and zygomorphy.
These two research results have recently published in Plant Systematics and Evolutioen titled with “Floral development of Phyllanthus chekiangensis (Phyllanthaceae), with special reference to androecium and gynoecium” and International Journal of Plant Sciences, with “Floral Development of Stephania (Menispermaceae): Impact of Organ Reduction on Symmetry”, respectively.
One selected figure of Phyllanthus chekiangensis floral development
Simplified cladogram of Menispermaceae based on molecular data
One selected figure of Stephania floral development
