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Systematic position of the enigmatic genus Sheareria ( Asteraceae)—evidence from molecular, morphological and cytological data

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Abstract:

The systematic position of the monoecious rheophyte, Sheareria (Asteraceae), a genus endemic to China, has been long disputed and never rigorously examined. In this study, two molecular datasets (trnL-F, ITS), plus morphological and cytological characters, were used to assess the systematic position of Sheareria. The broader phylogenetic analyses based on the trnL-F data placed Sheareria in the tribe Astereae with strong support. This placement was also supported by the lanceolate style, “Asteroid type” ligule epidermis, yellow anthers, green achenes, and basic chromosome number of x = 9. Analysis of the tribe Astereae based on the ITS dataset showed that Sheareria and three East Asian genera (Kalimeris, Aster, Rhynchospermum) formed a strongly supported clade characterized by flat, 2-ribbed, glandular disc achenes. Detailed morphological comparisons indicate that Sheareria is more similar to Kalimeris than to Rhynchospermum. Within this clade, Sheareria is distinguished from other genera by its monoecious breeding system (vs. gynomonoecious). Based on fossil and geological evidence, the development of monoecy in Sheareria is discussed. Within Sheareria, only one species, S. nana, is recognized; S. leshanensis, a newly described species, is placed in synonymy.

Keywords: ASTEREAE; CYTOLOGY; MOLECULAR PHYLOGENY; MORPHOLOGY; SHEARERIA

Document Type: Research Article

Affiliations: 1: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, the Chinese Academy of Sciences, Beijing 100093, China;, Email: gaotg@ibcas.ac.cn 2: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, the Chinese Academy of Sciences, Beijing 100093, China 3: Department of Biology, University of Memphis, Memphis, Tennessee 38152, U.S.A. 4: Kunming Institute of Botany, the Chinese Academy of Sciences, Kunming 650204, China

Publication date: August 1, 2009

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