Cytology and its systematic implications in Sinosenecio (Senecioneae-Asteraceae) and two closely related genera
2011
Liu, Ying | Yang, Qin-Er
Chromosome morphology and number in 28 species of Sinosenecio, two of Tephroseris and one of Nemosenecio (Senecioneae-Asteraceae) from China were investigated. Sinosenecio is revealed to have four basic chromosome numbers: x = 13, 24, 29, and 30, with 24 and 30 being predominant and 13 and 29 each occurring in one species only. The incidence of polyploidy is low in the genus. The karyotypes are all rather symmetrical and generally quite uniform in the species of similar chromosome number in respect of chromosome constitution, albeit with some variation in chromosome size among species. The pattern of basic chromosome numbers is largely congruent with results of floral micromorphological and molecular phylogenetic studies, and strongly indicates that Sinosenecio as currently construed is a polyphyletic group, badly needing a taxonomic re-circumscription at the generic level. We propose that only those Sinosenecio species with x = 30 should be retained in the newly defined genus, whereas those with x = 24 (rarely 13) (except for S. newcombei and S. koreanus which may find a home in Tephroseris) may be described as a new genus or preferably transferred to the genus Nemosenecio, and that S. hainanensis, the only Sinosenecio species having x = 29 and a suite of unique morphological and palynological characters, should be described as a new monospecific genus, Hainanecio, possibly positioned in the subtribe Senecioninae. When Sinosenecio is re-circumscribed in this way, not only does the genus Sinosenecio itself tend to be monophyletic, but the subtribe Tephroseridinae, which is composed of Nemosenecio, Sinosenecio, and Tephroseris, also may consequently become a better characterized and thus more acceptable group.
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