|其他摘要||Apiaceae (Umbelliferae) are a large and readily identifiable family of flowering plants, with subfamily Apioideae being the largest and most taxonomically complex (404 genera, 2827--2935 species). China is one of four major distribution centers of Apioideae, with 95 genera and 579 species recognized. In this study, we investigated the phylogenetic relationships of Apiaceae subfamily Apioideae mainly distributed in China including many endemics from the Hengduan Mountains, while ascertain or confirm the phylogenetic placements of all ten Chinese endemic genera by means of morphology, cytology and molecular systematics. Furthermore, chromosome evolution and biogeography of Chinese Apioideae were discussed. The main results are summarized as follows:
Karyological studies on seven genera, i.e. Ligusticum、Cyclorhiza、Tongoloa、Carum、Oenanthe、Pternopetalum and Chamaesium were carried out. All ten species of Ligusticum have the same basic chromosome number, x =11, but they could be differentiated by their karyotype formula and quantitative parameters of the karyotypes. L. capillaceum and L. pteridophyllum are tetraploid with the chromosome number of 2n = 4x = 44, other species are diploid with the chromosome number of 2n = 2x = 22. Our cytological results suggest that polyploidy did not play an important role in the chromosome evolution of Ligusticum. Ligusticum has great diversification in northwestern Yunnan of China, so this region is probably the most diversified center for it.
Maximum parsimony and Bayesian analyses of partitioned nrDNA ITS and cpDNA data sets or the combined molecular data, revealed a robust and well resolved phylogeny: (1) The phylogenetic placements of all ten Chinese endemic genera are resolved: Chuanminshen allies with Changium and Cyclorhiza in tribe Komarovieae; Notopterygium and Sinolimprichtia along with many other taxa of Sino-Himalayan distribution comprise a well-supported East-Asia clade, Notopterygium is paraphyletic, with the Chinese endemic species Vicatia bipinnata and Haplosphaera phaea arising from within it; Chaerophyllopsis finds affinity within tribe Scandiceae subtribe Scandicinae; Harrysmithia falls within the Acronema Clade; Melanosciadium embeds in Angelica in tribe Selineae, and Dickinsia is confirmed as a member of Apiaceae subfamily Azorelloideae; On the basis of phylogenetic analyses of ITS data, Nothosmyrnium allies strongly with tribe Pimpinelleae, while the results of MP and BI analysis of cpDNA data are equivocal in its placement; (2) Three major clades heretofore unrecognized in the subfamily were revealed (Acronema Clade, Chamaesium Clade, Sinodielsia Clade) and one (East Asia Clade, or the Physospermopsis Clade) was expanded considerably from its previous circumscription. The Acronema Clade was a well-supported sister group to tribe Scandiceae; the Chamaesium Clade occupied a basal and isolated position within the subfamily; the Sinodielsia Clade was either sister group to Ligusticum acuminatum Franch., or paraphyletic to tribe Apieae depending upon the analysis; and the East Asia Clade was a sister group to the Komarovia Clade; (3) The Acronema Clade includes species with an almost exclusively east Asian distribution, although its members are morphologically very heterogeneous and taxonomically complex, the same for the East-Asia Clade. These two Clades all belong to the East Asian Phytogeographycal type; (4) Several genera were confirmed as monophyletic, e.g. Pternopetalum, Chamaesium, Cyclorhiza. A large number of genera, which are notoriously difficult to define, having diffuse generic boundaries and heterogeneous patterns of variation (e.g., Ligusticum、Peucedanum、Physospermopsis、Pimpinella、Pleurospermum、Sinocarum、Tongoloa and Trachyspermum etc.) were not monophyletic based on our present study; (5) Sinodielsia、Meeboldia and Vicatia are distinct and distantly related, Peucedanum delavayi, phylogenetically distant from Sinodielsia and Meeboldia and united with three Ligusticum species in tribe Selineae; (6) Apiaceae subfamilies Saniculoideae, Azorelloideae, and Mackinlayoideae are each monophyletic, and show successive sister group relationships to subfamily Apioideae.
This is the first study to incorporate a broad sampling of Chinese endemics from Apiaceae subfamily Apioideae. Aside from providing a framework for taxonomic revisions, the phylogenetic structure recovered in this study for subfamily Apioideae will lay the foundation for future investigations of evolutionary patterns of morphological characters and biogeography. For Acronema clade and East-Asia clade, further sampling is necessary, as well as the acquisition of additional sequence data from the chloroplast genome to resolve distal relationships within the subfamily, before a comprehensive classification can be obtained.
Based on evidence from morphology, molecular phylogeny and biogeography, while considerring the congruency of relationships and high branch support, Komarovia Clade and Chamsesium Clade are recognized at the tribal rank, i.e. Komarovieae J. Zhou & S. R. Downie and Chamaesieae J. Zhou & F. D. Pu. The monotypic tribe Chamaesieae represents one of the earliest diverging lineages of subfamily Apioideae in Asia.
The family Apiaceae is widely distributed across temperate regions and especially in Central Asia, with two distribution centers (one is Mediterranean area, the other is western United States and Mexico). Based on previous studies, the ancetstor of the two largest subfamiles of Apiaceae (Apioideae and Saniculoideae) may have evolvd in southern Africa.
In our analyses, ten Chinese endemic genera were dispersed into seven major clades (Pimpinelleae, Acronema Clade, Selineae, Komarovieae, Scandiceae, East- Asia clade and Azorelloideae), represented different evolutionary stage of Apiaceae. The phylogenetic placements of Dickinsia, Changium, Chuanminshen, Cyclorhiza, Sinolimprichita and Notopterygium within Apiaceae are relatively basal, so belived to be paleo-endemic genera; Chaerophyllopsis, Harrysmithia, Mlanosciadium and Nothosmyrnium are in a position relatively distal, and may belong to neo-endemic genera. According to the phylogenetic placement and distribution of endemic genera, Yunnan and Sichuan Provinces of Kangdian Ancient Land are probable the secondary evolutionary centers for Chinese Apiaceae. One the one hand, the Tibetan plateau, with its dramatic variations in topography and climate, reserved the ancient elements of the family; on the other hand, the uplift of Tibetan plateau in Tertiary, contribute to the diversity of Apiaceae and some new taxa occurrence.
5. Chromosome evolution in subfamily Apioideae
Optimization of currently available chromosome information for subfamily Apioideae onto the phylogenies indicates: (1) x= 11（plesiomorphy）occurred in most genera of Komarovieae through Selineae; (2) The plesiomorphy x= 6 is maintained in tribe Chamaesieae, and the state reverses to x= 6 from the ancestor with x= 11 in Sium and Oreomyrrhis; (3) In Tongoloa silaifolia, Anthriscus sylvestris and Torilis japonica, x= 8 is autopomorphic; (4) x= 9 is synapomorphic in Pleurospermeae, Pimpinelleae and Pternopetalum; (5) x= 10 originated multiple times independently in Apioideae, and is autopomorphic for Nothosmyrnium; (6) In phylogenetic trees, Pimpinella species were dispersed into three major clades: taxa with x= 11 united with Selineae; taxa with x= 9 fell into the tribe Pimpinelleae; and taxa with x= 10 comprise a subclade (Chinese Pimpinella subclade) of East-Asia Clade. That is, the basic chromosome number of each coincide with their phylogenetic placement; (7) In our analysis, Pleurospermum species were fell into Pleurospermeae with x= 9 and Acronema Clade with x= 11. However, the chromosome information for Pleurospermum is insufficient to discern its infrageneric taxonomic treatment.|