| Euonymus (Celastraceae) is a cosmopolitan genus containing about130species. It has its species diversity centered in East Asia, particularly in China, and few species can be found in America, Africa and Australia. This genus exhibits a complex pattern of morphological variation, making its taxonomy difficult. Monophyly of the genus remains uncertain, and evolutionary implication of the infrageneric division and delimitation of many species are debatable. In this study, we sampled a total of62accessions representing48species/taxa covering a broad range of diversity of the genus and its allies. We first investigated the phylogeny of Euonymus using DNA sequences of multiple nuclear and plastid markers (nrITS, nrETS, and chloroplast psbA-trnH and rpl36f-rps8r, trnC-petNlr), and then used this phylogeny to discuss the circumscription and classification of the genus in combination with evolution of fruit characters, which has been used as an important criterion for the generic subdivision. The resultant data revealed the monophyly of Euonymus sensu lato with inclusion of Glyptopetalum, resolved the major lines of phylogeny of the genus, and clarified the echinate and winged capsules each as lineage-specific. Therefore, among the five sections accepted by Flora of China, only Sect. Echinococcus (with spiny fruits) and Sect. Kalonymus (with winged fruits) correspond to the molecular grouping. The globose capsule may represent an ancestral character state, and the other types of fruits, i.e., the shallowly to deeply lobed capsules, may belong to a broad range of continuous variation derived from the globose.Furthermore, we studied the character evolution of the inflorescences architecture of Celastraceae. Celastraceae are characterized by a cymose pattern of inflorescence ramification. Under this basic pattern, many inflorescence forms have been described within the family, e.g., dichasium, monochasium, pleiochasium, botryoid, thyrsoid, fascicle. We found in C. orbiculatus that the reduction of subtending leaves of the axillary dichasia on a developing flowering shoot made it become a terminal thyrsoid. A dichasium in the leaf axil as commonly seen in Euonymus is the most frequent type of inflorescence in Celastraceae. An analysis of character evolution suggested that a dichasium is the ancestral state for Celastraceae. Therefore, within Celeastaceae, an axillary dichasium may be the basic type or unit of inflorescences. Transitions from dichasium to thrysoid and other types of cymes, and even to solitary flowers might have occurred repeatedly in the family, probably a phenomenon of evolutionary convergence due to changing environmental conditions. The transision, especially the simplification of inflorescence ramification may be related with the activity of peduncle articulation which is a special structure of plants in many genera of Celastraceae. A flower may get abortive and drop at the articulation. This may result in the reduction of the number of flowers on an inflorescence, leading to varying simplified types of cymose inflorescences in the family Celastraceae. Therefore, the peduncle articulation may be an adaptive feature of plants to guarantee reproduction efficiency under environmental constrain.The present molecular phylogenetic data not only provides insightful information for study on evolution and classification of the Euonymus species, but for understanding evolution of some important morphological characters of the genus or even of the whole family Celastraceae. |
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