A PHYTOGEOGRAPHICAL ANALYSIS OF TAXUS (TAXACEAE) BASED ON LEAF ANATOMICAL CHARACTERS
A phytogeographic analysis of 845 Taxus specimens is presented based on leaf anatomical characters for the number of stomata rows in a stomata band and the number of epidermal cells that lack papillae between the leaf margin and stomata band. The specimens are arranged by continent, country, state o...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.691.9196 http://www.worldbotanical.com/images/ARS+NCI+Active+Plants/22_Spjut_PhytogeographicalTaxus291-332Web.pdf |
| Summary: | A phytogeographic analysis of 845 Taxus specimens is presented based on leaf anatomical characters for the number of stomata rows in a stomata band and the number of epidermal cells that lack papillae between the leaf margin and stomata band. The specimens are arranged by continent, country, state or province, and species, and represented geographically on three maps: (1) North America, (2) the Euro-Mediterranean, and (3) Asia. Taxus is least diverse and most distinct taxonomically in North America, and most diverse and least distinct taxonomically in southwest China. Stomata data show several clines in North America, an obvious south to north decrease for the Mesoamerican yew (T. globosa) and Pacific NW yew (T. brevifolia) populations combined, and a less obvious reverse cline for the Canada yew (T. canadensis). The results are discussed in review of other paleobotanical data. It is suggested that Taxus immigrated to North America from Asia across a Pacific land connection during the Cretaceous, and from Europe to North America across North Atlantic land bridges during the Tertiary. The low diversity of Taxus in North America is suggested to be the result of the K/T extinction event. In the Euro-Mediterranean, evolution of Taxus is suggested to have been impacted more by extinction as a result of climatic changes during the Tertiary, and by hybridization during the Pleistocene. The greater diversity in SW China is indicated to be the result of less extinction there and more frequent hybridization during the Pleistocene, not only among authochtonous species, but also allochtonous species as a result of the Himalayan uplift. |
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