|其他摘要||The tribe Gaultherieae, consisting of six genera (ca. 250 species), forms a monophyletic group within subfamily Vaccinioideae of the Ericaceae. It exhibits a distinctive amphi-Pacific distribution and the bulk of the distribution is tropical and subtropical. The intergeneric and infrageneric relationships of Gaultherieae based on morphological study have been debated for a long time. The monophyly of Gaultherieae has been confirmed by preliminary molecular studies up to now, while the systematic relationships in most genera are still unclear and Gaultheria, the largest genus within this tirbe, was determined as a paraphyletic group. Comprehensive sampling is required to further phylogenetic study.
In this dissertation, palynology and seed morphology of Gaultherieae were studied for employing more critical characters (synapomorphies) for the reclassification. The phylogeny of Gaultherieae was reconstructed based on the molecular data (ITS, rpl16, trnL-F, trnG-S and matK) with intensive sampling. Origins and biogeographic patterns in Gaultherieae were preliminarily discussed.
The pollen morphology of 86 samples from 84 species of Gaultheria and closely related genera of the subfamily Vaccinioideae, Chamaedaphne, Craibiodendron, Diplycosia, Eubotrys, Gaylussacia, Leucothoe, Lyonia, Oxydendrum, Pieris, Satyria, and Vaccinium was investigated with light and scanning electron microscopy. The tetrahedral size, aperture and exine ornamentation (apocolpia and mesocolpia) of pollen grains are variable. Viscin threads on the pollen grains of members of Gaultheria are reported for the first time. Infrageneric relationships of Gaultheria are discussed on the palynological basis. Pollen data support the sister relationships between Satyria and Vaccinium and between Chamaedaphne and Eubotrys as reported by previous molecular phylogenetic analyses. The evolution of pollen characters is traced by character optimization. It seems that an evolutionary trend of mesocolpium ornamentation within Vaccinioideae from granulate through granulate–rugulate to rugulate is apparent.
2. Seed morphology
The seed morphology of 90 samples from 83 species of the tribe Gaultherieae, represented by Chamaedaphne, Diplycosia, Eubotryoides, Eubotrys, Gaultheria, Leucothoe, and Tepuia and its related tribes Andromedeae represented by Andromeda and Zenobia and Vaccinieae by Satyria was investigated with stereoscopic and scanning electron microscopy. The seeds exhibit high morphological diversity in shape, color, size, wing, hilum region, primary ornamentation and epidermal cells. Seed characters corroborate the delimitation of Andromeda, Chamaedaphne, Leucothoe, Satyria, and Zenobia, and some classifications within Gaultheria. Small seeds trend to be evolved from larger ones, and areolate seed coats may have been evolved from a reticulate primary ornamentation. The presence of seed wings, a flattened and ellipsoid-mucronate shape, and distinct hilum protuberances are synapomorphies for the clade comprising Eubotryoides and Leucothoe. Obliquely pyramidal seed shape, small seed size, and areolate primary ornamentation could be potential synapomorphies for some major clades of Gaultherieae. Seeds of the Gaultherieae from East Asia, temperate North America, and the Pacific are more diverse than those from tropical America. Samples from the eastern Himalaya possess the highest variation in seed morphology. The wings and bulging edge cells observed in seeds of Leucothoe suggest wind dispersal.
3. Molecular phologenetics within Gaultherieae
The phylogeny of 121 taxa from 105 species within the whole tribe Gaultherieae was estimated from separate and combined analyses of four cpDNA sequence data sets (rpl16, trnL-F, trnG-S and matK). Both Gaultherieae and the wintergreen group are monophyletic with strong support. The monophyly of Leucothoe and Eubotrys is also supported, respectively. Diplycosia and Tepuia are monophyletic but nested within other species of Gaultheria. Eubotryoides was not supported by molecular evidence while a clade comprising species of Eubotryoides and Leucothoe are the earliest diverged within Gaultherieae, with Eubotrys and Chamaedaphne as the next diverged one. The wintergreen group consists of five major clades: an Asian-Amrican Clade, a North Amrican-Japan Clade, a Sino-Himalayan Clade, an Oceania-Latin American Clade and an East Asian-American Clade. Reticulate evolution may be involved in the speciation of G. leucocarpa, which might have spread from China to the Southeast Asia via Southeast Yunnan. All the Oceanian samples form a clade with strong support. G. insipida, G. strigosa, G. buxifolia and G. antarctica might be the phenotypic and genetic transitions between South American and Oceanian taxa.
4. Molecular phologenetics within the Sino-Himalayan Clade
The phylogeny of 90 taxa from 33 species (including 2 unknown species) within the Sino-Himalayan Clade was estimated from separate and combined analyses of five DNA sequence data sets (ITS, rpl16, trnL-F, trnG-S and matK). The Sino-Himalayan Clade was resolved to consist of two subclades: the large-leaved one and the small-leaved one. Rapid evolutionary radiation may be involved in the large-leaved subclade due to the low resolution topology of some species. It is likely that the large-leaved Gaultheria pyrolifolia with might be a hybrid and the small-leaved G. pyrolifolia with might be a parent. The peculiar relationship between G. notabilis and G. nummularioides may be an appropriate example for hybrid speciation. G. notabilis might be a recent hybrid. Conflict of the systematic position of G. nummularioides RBGE35 between nuclear and chloroplast genes suggested ThybridizationT and Tpolyploidy, orT introgression of chloroplast DNA occurs during the evolution of the G. nummularioides complex. Reticulate evolution may also be common in the small-leaved subclade. The discordance of the molecular and morphological patterns in the small-leaved subclade could be results of ecological adaption.
5. Preliminary study on the biogeography of Gaultherieae
By tracing the geographic distribution onto the Bayes phylogeny from combined analysis with parsimony optimization, a North American origin was assigned to the base of the tribe. It positively supports the boreotropics hypothesis for the origin of the Ericaceae. Asia might be the center of origin for some groups within Gaultherieae. The close phylogenetic relationships among those East Asian – North American samples within Sect. Amblyandra and Ser. Hispidulae to some extent suggest the “Land bridge” explanation for the dispersal of Gaultherieae. The Oceanian taxa may be derived from the temperate South American ancestors. It could be inferred that the Gaultherias in the temperate South America may have dispersed towards both tropical South America and Oceania (New Zealand, Australia). The speciation of genus Diplycosia might be resulted from the vicariance. Long-distance dispersal and vicariance may facilitate evolution of the tribe Gaultherieae.|