Cytology and Its Systematic Implications in Sinosenecio (Senecioneae-Asteraceae) and Two Closely Related Genera
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Plant Syst Evol (2011) 291:7–24 DOI 10.1007/s00606-010-0365-3 ORIGINAL ARTICLE Cytology and its systematic implications in Sinosenecio (Senecioneae-Asteraceae) and two closely related genera Ying Liu • Qin-Er Yang Received: 25 March 2010 / Accepted: 6 September 2010 / Published online: 8 October 2010 Ó Springer-Verlag 2010 Abstract Chromosome morphology and number in 28 and a suite of unique morphological and palynological species of Sinosenecio, two of Tephroseris and one of characters, should be described as a new monospecific Nemosenecio (Senecioneae-Asteraceae) from China were genus, Hainanecio, possibly positioned in the subtribe investigated. Sinosenecio is revealed to have four basic Senecioninae. When Sinosenecio is re-circumscribed in chromosome numbers: x = 13, 24, 29, and 30, with 24 and this way, not only does the genus Sinosenecio itself tend to 30 being predominant and 13 and 29 each occurring in one be monophyletic, but the subtribe Tephroseridinae, which species only. The incidence of polyploidy is low in the is composed of Nemosenecio, Sinosenecio, and Tephrose- genus. The karyotypes are all rather symmetrical and ris, also may consequently become a better characterized generally quite uniform in the species of similar chromo- and thus more acceptable group. some number in respect of chromosome constitution, albeit with some variation in chromosome size among species. Keywords Asteraceae Á Chromosome number Á The pattern of basic chromosome numbers is largely con- Cytotaxonomy Á Karyotype Á Polyphyly Á Sinosenecio gruent with results of floral micromorphological and molecular phylogenetic studies, and strongly indicates that Sinosenecio as currently construed is a polyphyletic group, Introduction badly needing a taxonomic re-circumscription at the gen- eric level. We propose that only those Sinosenecio species Sinosenecio B. Nord. (Senecioneae-Asteraceae) was seg- with x = 30 should be retained in the newly defined genus, regated as an independent genus from the notoriously whereas those with x = 24 (rarely 13) (except for heterogeneous Senecio by Nordenstam (1978) on the basis S. newcombei and S. koreanus which may find a home in of its palmately veined, petiolate leaves with the lamina Tephroseris) may be described as a new genus or prefer- distinct from the petiole, ecalyculate involucres, campan- ably transferred to the genus Nemosenecio, and that ulate limb of the disc florets, polar or polar and radial S. hainanensis, the only Sinosenecio species having x = 29 anther endothecial cell wall thickenings, and cylindrical filament collars. Jeffrey and Chen (1984) accepted Nor- denstam’s concept of the genus, and made a monographic treatment. They recognized 31 species in the genus, which Q.-E. Yang (&) they divided into two sections, viz.: sect. Sinosenecio and Key Laboratory of Plant Resources Conservation and sect. Phyllocaulon C. Jeffrey & Y. L. Chen. Section Sustainable Utilization, South China Botanical Garden, Sinosenecio is characterized by strictly polar endothecial Chinese Academy of Sciences, Xingke Road, Tianhe District, Guangzhou 510650, People’s Republic of China thickenings and the presence or absence of cauline leaves, e-mail: [email protected] whereas sect. Phyllocaulon has radial or radial and polar endothecial thickenings and cauline leaves. Within both Y. Liu sections they furthermore proposed some subsections and State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, series, mainly with reference to the presence or absence of Beijing 100093, People’s Republic of China cauline leaves or of pappus, and ovary and achene 123 8 Y. Liu, Q.-E. Yang pubescence (Jeffrey and Chen 1984). This genus is cur- been invaluable in the study of plant systematics rently a medium-sized group of approximately 40 species, (Watanabe et al 1995). Despite the potential systematic with the transfer of a species from Senecio (Janovec and importance of chromosomal data for Sinosenecio, this Barkley 1996) and continued description of new species genus is nevertheless very poorly known cytologically. (Chen 1988, 1995, 1999; Liu 2000; Zhang et al. 2008; Liu Lee (1969) reported the chromosome number of S. kore- et al. 2009, 2010; Liu and Yang 2010). All the species are anus (Kom.) B. Nord. as n = 23 under the name Senecio restricted to China, Korea, and Indo-China (Nordenstam koreanus Kom., this being the first chromosome count for 1978; Jeffrey and Chen 1984; Chen 1999) except one, Sinosenecio. This number has long been cited as a basic S. newcombei (Greene) J. P. Janovec & T. M. Barkley, a chromosome number for the genus (Jeffrey and Chen species endemic to the Queen Charlotte Islands, BC, 1984; Jeffrey 1992; Nordenstam 2007; Nordenstam et al. Canada (Janovec and Barkley 1996) (its generic affiliation, 2009). Liu (1999), in his unpublished Ph.D. dissertation, however, is still a controversial matter; see below). The checked the chromosomes of six taxa in the genus and central and southwestern parts of China are the center of reported 2n = 24 for S. homogyniphyllus (Cumm.) species diversity for this genus, with nearly all of the B. Nord. and S. oldhamianus (Maxim.) B. Nord., 2n = 48 species occurring there (Chen 1999). In the tribe Sene- for S. bodinieri (Vaniot) B. Nord. and S. septilobus cioneae, Sinosenecio is generally considered to be (Chang) B. Nord., 2n = 60 for S. subcoriaceus C. Jeffrey most closely related to Nemosenecio and Tephroseris & Y. L. Chen, and 2n = 72 for S. globigerus (Chang) (Nordenstam 1978, 2007; Jeffrey and Chen 1984; Chen B. Nord. var. adenophyllus C. Jeffrey & Y. L. Chen. 1999; Pelser et al. 2007; Wang et al. 2009; Nordenstam Strangely, Liu (2004) cited the chromosome number of et al. 2009). Jeffrey and Chen (1984) established the sub- S. globigerus as 2n = 60, stating that the material was tribe Tephroseridinae to accommodate the three genera, but collected from Nanchuan, Chongqing, China, and making other authors (Jeffrey 1992; Bremer 1994; Nordenstam reference to his Ph.D. dissertation. Actually he did not 2007; Pelser et al. 2007; Nordenstam et al. 2009), albeit report the chromosome number of this taxon in the dis- admitting their closest affinity, did not recognize this sertation; the only taxon with the number 2n = 60 subtribe because of its lack of diagnostic characters and reported therein was S. subcoriaceus. In fact, the typical its phylogenetic position deeply nested in the subtribe variety of S. globigerus, var. globigerus, has not yet been Tussilagininae sensu Jeffrey and Chen (1984). found in Nanchuan (Chen 1999), and only another variety Recently, the monophyly of Sinosenecio has been seri- under the species, var. adenophyllus, occurs there. This ously challenged by molecular systematic data. The transfer variety, as mentioned above, was reported to have of S. newcombei from Senecio to Sinosenecio was not sup- 2n = 72 by Liu (1999). Therefore, the record of 2n = 60 ported by ITS sequence data (Golden et al. 2001); this spe- for S. globigerus is a very dubious count. Wang et al. cies was shown to be more closely related to North American (2009) regarded the number 2n = 24 for S. homogyni- Tephroseris species than to the Asiatic Sinosenecio species. phyllus also as a miscount. Most recently, Zhang et al. The most recent molecular phylogenetic studies, though all (2008) reported the chromosome number of S. jishouensis based on limited species sampling, have shown that some D. G. Zhang, Y. Liu & Q. E. Yang as 2n = 48 and 96, Liu Sinosenecio species are nested in a well supported clade et al. (2009, 2010) reported the number for both S. baoj- with Nemosenecio and Tephroseris (‘‘tephroseroid’’clade = ingensis Y. Liu & Q. E. Yang and S. hupingshanensis subtribe Tephroseridinae) whereas others are clustered with Y. Ying & Q. E. Yang as 2n = 48, and Liu and Yang typical Tussilagininae (‘‘tussilaginoid’’) genera, for example (2010) reported the number for S. yilingii Y. Liu & Cremanthodium, Farfugium, Ligularia, Parasenecio, Peta- Q. E. Yang as 2n = 60. The remaining species in the sites, Syneilesis, and Tussilago (Pelser et al. 2007; Wang genus have not as yet been investigated cytologically. et al. 2009). Wang et al. (2009) have discussed in detail the The main objective of the work discussed in this paper incongruence between the ITS phylogeny and generic was to examine extensively the chromosome morphology delimitation in the Nemosenecio–Sinosenecio–Tephroseris and number of Sinosenecio, and to evaluate the significance assemblage, pointing out that neither Sinosenecio nor of chromosomal data for systematic consideration of this Tephroseris as currently construed is a monophyletic group, genus with special reference to evidence from floral and both need a generic re-circumscription. micromorphological observations and recent molecular As chromosome morphology and number within genera systematic studies. Two Tephroseris species and one are often remarkably constant, and many of the groups that Nemosenecio species were also included in this study, for have distinctive chromosome numbers are among the most comparison of the chromosomal characters of the three readily defined taxonomically, chromosomal data have closely related genera. 123 Cytology in Table 1 Source of material studied, chromosome numbers, and karyotype formulae Taxon Locality and voucher 2n Karyotype formula Chromosome TKL (lm) A1 A2 Stebbins’s NMC Figure length range type (lm) Sinosenecio Sinosenecio eriopodus Yongshun, Hunan, Q. E. Yang et al. 641 60 34 m ? 26sm 3.18–1.38 125.00 0.37 0.19 2B 8 1 S. hederifolius Shennongjia, Hubei, Y. Liu 2008007 60 40 m ? 14sm ? 6st 3.16–1.26 117.79 0.35 0.20 2B 5 2, 51 S. rotundifolius Songpan, Sichuan, Y. Liu & Deng 2009086 60 44 m ? 16sm 4.08–1.53 142.90 0.29 0.22 2B 3 3, 52 S. ligularioides Baoxing, Sichuan, Y. Liu & T. Deng 2009071 60 2 4 S. subrosulatus Maoxian, Sichuan, Y. Liu & T. Deng 2009081 60 52 m ? 8sm 3.44–1.36 130.91 0.17 0.21 2B 5 5, 53 S.