Evolution Of Floral Development Characters In Ranunculaceae

Flowers are the reproductive organs of angiosperms, and they play a crucial role in the diversity of angiosperms. The issue of floral origin and evolution has been a long-standed question for the systematic and evolutionary botanists. There is much more important evolutionary information during floral devlopment comparing with the mature structures. Ranunculaceae, which links basal angiosperms and core eudicots, has shown great floral morphological diversity. Ranunculaceae is thus ideally suited for examination of floral origin and evolution. Reconstruction of the phylogeny and bayesian dating are conducted based on three regions in plastid and evolution of floral developmental characters are analysed, and the results are as follows:(1) The development of flowers of 12 species from 12 genera,6 tribes in Ranunculaceae were studied using scanning electron microscopy (SEM).(2) Plastid (rbcL, matK and trnL-F) sequences were analyzed with parsimony, likelihood, and bayesian inference. Ranunculoideae is paraphyletic and Thalictroideae is nested within the Ranunculoideae clade. The Thalictroideae has not autapomorphy in flora development and should be merged with Ranunculoideae. Ranunculaceae is thus comprised of four subfamilies, i.e. Glaucidioideae, Hydrastidoideae, Coptidoideae and Ranunculoideae.(3) Divergence times of disjunct lineages were estimated with relaxed Bayesian dating. The divergence of the four subfamilies occurred 90-68.97 Ma (late Cretaceous); the divergence of the tribes occurred 62.22-51.3 Ma (early Paleocene to early Eocene); the divergence of the genera occurred 38.55-5.17 Ma (late Eocene to Miocene). The ancestor taxa of the subfamilies maybe the relictual lineage after the mass extinction in Cretaceous. The quick radiation of the tribes and genera may be related with temperature warming.(4) Evolution of the floral developmental characters was assessed by tracing these characters onto Bayesian trees using the Trace Character Over Trees option in the program Mesquite, and the results showed that:Parallel evolution occurs for different characters in different taxa. The petals are present in the ancestor node of Coptidoideae and Ranunculoideae, while the petals are absent in several unrelated clades, which is the results of secondary missing and parallel evolution. The petals appear again in some species of Clematis and Pulsatilla is the result of secondary acquisition. There are no appendages during the petal development in the ancestor of Coptidoideae and Ranunculoideae, and the nectar tissue appears on a specific region. During the petal development in the ancestor of Ranunculoideae, a shallow depression appears firstly in the centre of the ventral side, then two bulges arise in a short succession at the base of the depression. Only one bulge at the base of the depression is considered to be derived. The two bulges always become connate and then fuse with the blade and forming a tubular, spur-shaped or sac shaped structure where the nectar tissue appears. The single bulge always develops into the small scale beneath which the nectar tissue appears. We consider that the developmental result of the appendage may be a highly modified structural and functional feature for concealing the nectar and controlling the access of the visitors.Epeltate carpel is the plesiomorphy while ascidiate carpel in unrelated clades is the apomorph in Ranunculaceae. The moderate number of carpels is the plesiomorphy and less or more numbers are derived. The less number of carpels is related with whorled phyllotaxis and the large number is related with spiral phyllotaxis.Radial symmetry is plesiomorphy in Ranunculaceae. Bisymmetry in Delphinieae is caused by the reduction of several petal primordia. Bisymmetry is thus derived characters and the autapomorphy of the tribe Delphinieae.Wholed phyllotaxis for floral organs is the plesiomorphy in Ranunculaceae, and the floral phyllotaxis are spiral in the ancestral taxa of Coptidoideae and Ranunculoideae. The whorled phyllotaxis are present in different clades, which is the result of parallel or convergent evolution. The irregular phyllotaxis in Ranunculeae and Anemoneae is caused by redundant stamens and carpels.