Studies On Phylogeography Of Croomia And Phylogeny Of Croomia And Its Allies

Stemonaceae, composed of 4 genera and about 32 species, is a small monocot family. The members of it are distributed throughout the monsoon region of eastern Asia, with a single species of Croomia in the southeastern United States. The family is distinct morphologically from other monocotyledons by the flowers with 4-merous or 5-merous tepals and stamens. This small family has attracted much interest of plant taxonomists and phylogeographers. It played an important role in the phylogeny of monocotyledon and the plants with reticulate vein.The haplotypes of trnL-F and atpB-rbcL noncoding regions of cpDNA were analysed to infer phylogeography and the history of speciation, and the possible refugia of Croomia. ISSR markers were used to study the level and patterns of genetic diversity of Croomia. The phylogeny of the family and the relationships of the species of the Stemona were also studied here, based on matK, trnL-F, atpB-rbcL and ITS sequences data. The main results are listed as following:1. Phylogeographic study on CroomiaThe relationships and distribution of cpDNA haplotypes suggested that Croomia had been widely distributed in ancient eastern Asian and northern American; the origin and distribution center of Croomia were concentrated on the mountains comprised Mt.Huangshan and Mt.Tianmushan. The route of spread might be from China to Japan, then to ancient North American. Several putative Pleistocene refugia were inferred. The refugia of Croomia in China concentrated on Mt. Tianmushan and Mt. Huangshan. In Japan, the refugia were distributed in Kyushu, Shikoku and Kanto District. At least one refugium was inferred in USA.2. Genetic diversity of CroomiaThe results of inter-simple sequence repeat (ISSR) indicated that the genetic diversity of Croomia was very low. At the population level, the genetic diversity of C. japonica (PPB = 21.20%, H_pop= 0.0644, I = 0.0981, N_e=1.1077) was lower than that of C. heterosepala (PPB = 29.81%, H_pop= 0.0944, I = 0.1424, N_e=1.1613). But at the species level, the genetic diversity of C. japonica was higher than that of C. heterosepala. Strong differentiation among populations was found in both species (F_ST = 73.60% in C. japonica, and F_ST = 54.99% in C. heterosepala). The UPGMA phylogenic tree and principal components analysis (PCA) result showed that the populations of C. japonica in Japan were closer to C. pauciflora and C. heterosepala than the populations in China did. Significant positive correlation was found between genetic and geographic distance (r = 0.7, P <0.001).3. Preliminary studies on breeding system of C. japonicaCombined analysis of breeding system, results of multiple mating experiments and the pollen/ovule ratio (P/O) showed that the breeding system of C. japonica was self-compatible, and self-breeding was predominant in the wild populations. The P/O ratios varied among populations, indicating that sex allocation of different populations were variable. The genetic diversities of populations were obviously positively correlated to the P/O ratios. As the genetic diversity of rare plant populations is historical, the breeding system of C. japonica might be on the changing from cross-breeding to self-breeding. Some pollen germinated before being released from the anther. This phenomenon warrants further study.4. Phylogeny study on Croomia and StemonaThe relationship of the genus and the taxonomic placement of StemonaceaeThe phylogenetic tree of matK, trnL-F, atpB-rbcL and ITS sequences data indicated that it was natural to place Stemona and Croomia in one family. The matK-based phylogeny showed that Cyclanthaceae, Pandanaceae, Stemonaceaae and Velloziaceae formed a monophyletic clade (Pandanales). This supported that Stemonaceae should be separated from Liliales (or Dioscoreales) and placed in Pandanales. Affinities and speciation of the species in CroomiaThe two Asian species of Croomia were more closely related to each other than either is to Northern American species. C. japonica was presumed as the progenitor species, and C. pauciflora and C. heterosepala were presumed as the derivative species. As significant differentiation among populations, the populations of C. japonica in Japan were closer to C. pauciflora and C. heterosepala than those in China.Affinities of the species in StemonaFrom the molecular data, little difference was found between S. shandongensis and S. sessilifolia. Based on an examination of many specimens and a study of both wild and transplanted individuals, it suggested that morphological characters of S. shandongensis are within the variation range of S. sessilifolia. So the former was treated here as a new synonym of the latter.Combined analysis of sequence data showed that S. japonica was affinitive to S. sessilifolia, and they formed with S. mairei into one clade with high value of Bootstrap. S. javanica and S. parviflora, both distributed in tropic islands, showed a close relationship.5. Strategies for conservation of CroomiaBecause of few and small size of populations, high level of differentiation among populations and peculiar cpDNA haplotypes existed in different populations, all the populations of Croomia should be protected. A further management measure should aim at increasing the number of plants in small populations. Since Croomia can spread vegetatively via rhizomes in suitable habitats, a strategy seems feasible involving propagation via rhizome segments and tissue culture techniques, followed by cultivating in garden plots, and subsequent reintroduction into their original wild habitat.