Hainanecio, a New Genus of the Senecioneae, Asteraceae from China
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Botanical Studies (2011) 52: 115-120. SYSTEMATICS Hainanecio, a new genus of the Senecioneae, Asteraceae from China Ying LIU2 and Qin-Er YANG1,* 1Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Xingke Road, Tianhe District, Guangzhou 510650, China 2State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China (Received March 31, 2010; Accepted June 10, 2010) ABSTRACT. Hainanecio Y. Liu & Q. E. Yang, a new genus of Senecioneae, Asteraceae, from Hainan Is- land, China, is described based on Sinosenecio hainanensis (Chang & Tseng) C. Jeffrey & Y. L. Chen. Distin- guishing characters include pinnately-veined, ovate to obovate leaves, hemispherical involucres, white florets, apically acuminate and often 2-denticulate rays, basic chromosome number of x = 29, typically triporate pol- len, and helianthoid type of pollen wall ultrastructure. Keywords: Asteraceae; Hainanecio; New genus; Senecioneae; Sinosenecio; Taxonomy. INTRODUCTION pinnately-veined, ovate to obovate leaves (vs. palmately- veined, rounded, reniform to ovate or deltoid), hemispheri- Hainanecio Y. Liu & Q. E. Yang, based on Sinosenecio cal involucres (vs. obconic or campanulate), white florets hainanensis (Chang & Tseng) C. Jeffrey & Y. L. Chen (vs. yellow), and apically acuminate, often 2-denticulate from Hainan Island, China, is described as new. Our recent rays (vs. apically obtuse and 3-denticulate rays). Among systematic study of Sinosenecio B. Nord. (Senecioneae- these characters, the color of the flowers is worthy of Asteraceae) has indicated that this enigmatic species has a special note. In the protologue, Chang and Tseng (1974) series of unusual morphological, cytological, and palyno- described the flowers as being ‘probabiliter aurantiaceis’ logical characters, and thus definitely does not belong in (probably orange), but our field observations at two sites the genus Sinosenecio. on Hainan (including the type locality) revealed the flow- Hainanecio hainanensis, endemic to Hainan Island, ers to be white (Figure 2). All species of Sinosenecio have China (Figure 1), was considered to be the southernmost yellow flowers (Jeffrey and Chen, 1984; Chen, 1999), as occurring species of Sinosenecio (Jeffrey and Chen, 1984; do all the Chinese species of Senecio, in which the species Chen, 1999). Originally described as Senecio hainanensis was originally described (Jeffrey and Chen, 1984; Chen, by Chang and Tseng (1974), it was transferred to Sino- 1999). senecio by Jeffrey and Chen (1984) based on its scapiger- ous habit, strictly polarized anther endothecial cell wall thickenings, and tumid epappose achenes. Jeffrey and Chen (1984) regarded those characters in combination as characteristic of Sinosenecio, although they noted simul- taneously that the species was unusual in the genus in its pinnately veined, ovate to obovate leaves. The species has since been noted as anomalous within Sinosenecio (Chen, 1999; Zhang et al., 2008), but has until now been included within the genus. Our field and herbarium observations have confirmed and increased the number of morphological differences be- tween Hainanecio hainanensis and species of Sinosenecio: * Corresponding author: E-mail: [email protected]; Tel: +86-20-37094273; Fax: +86-20-37094273. Figure 1. Distribution of Hainanecio hainanensis (▲). 116 Botanical Studies, Vol. 52, 2011 7B, D). Surprisingly, the pollen grains of H. hainanensis are typically triporate, lacking the three noticeably wide colpi that are always present in pollen grains in Sinosene- cio (Figure 7E), and the tectum is smooth and perforate (Figure 7F). The pollen grains of other genera in the tribe Senecioneae have all been reported to be tricolporate (Stix, 1960; Skvarla and Turner, 1966; Skvarla et al., 1977; Vincent and Norris, 1989; Liu, 2002). Furthermore, SEM shows that the pollen grains of H. hainanensis are obvi- ously less densely echinate than those of other species of Sinosenecio examined. Under transmission electron microscopy (TEM), the structure of the pollen wall of all species of Sinosenecio, except H. hainanensis, are of the senecioid type (absence of internal foramina, Figure 8A-I), the commonest pollen type within the tribe Senecioneae (Nordenstam, 2007; Nordenstam et al., 2009). Unexpect- edly, the structure of the pollen wall of H. hainanensis is of the helianthoid type (presence of internal foramina, Figure 8J-L). In the Senecioneae, the helianthoid pollen Figure 2. Hainanecio hainanensis. A, Habit; B, Young capitula; type has been reported previously only in a few genera C, Capitulum (top view); D, Florets (left: disc floret; right: ray (Nordenstam, 2007; Nordenstam et al., 2009): Doroni- floret); E, Capitulum (bottom view), showing phyllaries; F, Rhi- cum (Skvarla et al., 1977; Liu, 2000) from the subtribe zome; G, Habitat. (All from Y. Liu 2008044, IBSC, PE). Doronicinae, Farfugium (Liu, 2000), Telanthophora and Robinsonecio (Bain et al., 1997) from the subtribe Tus- silagininae, Pericallis (Skvarla et al., 1977) and Packera Hainanecio hainanensis has truncate style arms with (Skvarla et al., 1977; Bain and Walker, 1995) from the marginal and apical papillae (Figure 3A), polarized and subtribe Senecionineae. Obviously, H. hainanensis can- radial endothecial cell wall thickenings, with the polarized not be referred to any of these six genera because of the ones being predominant (Figure 3B), and a short, cylindri- remarkable differences in other characters. cal filament collar (Figure 3C). These features have been Recent molecular phylogenetic studies, which did not previously observed in species of Sinosenecio (Norden- sample Hainanecio hainanensis, have shown that Sino- stam, 1978; Jeffrey and Chen, 1984; Liu, 1999; Zhang senecio is a polyphyletic group (Pelser et al., 2007; Wang et al., 2008; Liu et al., 2009). Jeffrey and Chen (1984) et al., 2009). Some species of Sinosenecio were found to reported the anther endothecial cell wall thickenings of H. be nested in a well supported clade with Tephroseris and hainanensis as being strictly polarized, but this was not confirmed in our study. Most notably, the anther apical appendage of H. hainanensis is ovoid and bubble-like in shape, with the abaxial cells obviously enlarged (Figure 3D). In all species of Sinosenecio the anther apical ap- pendages are ovoid, but not bubble-like, with the abaxial cells not enlarged (Liu and Yang, in prep.). During our study, the distinctive nature of Hainanecio hainanensis was strongly reinforced by observations of the chromosomes and pollen. The mitotic chromosome number of Hainanecio hain- anensis is 2n = 58 (Figure 3E), with a basic number of x = 29. The chromosomes range from ca. 1.8 to ca. 0.8 μm from the largest to the smallest. In contrast, the basic chro- mosome numbers in the species of Sinosenecio are pre- dominantly x = 24 and 30, rarely 13, and the chromosomes are larger, usually ranging from ca. 4.0 to ca. 1.2 μm (Liu and Yang, in prep.). Figure 3. Floral micromorphological characters (A, B, C, D) and mitotic metaphase chromosomes (E) of Hainanecio hainanensis. All the species of Sinosenecio examined, except A, Style-arms; B, Anther endothecial cell wall thickenings; C, Hainanecio hainanensis, have the same pollen external Filament collar; D, Anther apical appendage; E, Mitotic meta- morphology under scanning electron microscopy (SEM) phase chromosomes (2n = 58) (all from Y. Liu 2008044, IBSC, (Figures 4-7). The pollen grains are spheroid, tricolporate, PE). Scale bars: A, D = 100 μm; B = 25 μm; C= 50 μm; E = 5 echinate, with the tectum coarse and not perforate (Figure μm. LIU and YANG — Hainanecio, a new genus 117 Nemosenecio (‘tephroseroid’ clade = subtribe Tephrose- the generic delimitation in the Nemosenecio-Sinosenecio- ridinae), whereas others clustered with typical genera of Tephroseris assemblage, pointing out that neither Sino- Tussilagininae (‘tussilaginoid’), such as Cremanthodium, senecio nor Tephroseris as currently construed forms a Farfugium, Ligularia, Parasenecio, Petasites, Syneilesis, monophyletic group. Both are awaiting a generic recir- and Tussilago. Wang et al. (2009) have discussed in detail cumscription. The results of our phylogenetic analysis of the strong incongruence between the ITS phylogeny and the ITS data set of Sinosenecio, which included a broader taxon sampling, have also revealed the polyphyly of Sino- senecio and indicated that H. hainanensis is a member of subtribe Senecioninae, only distantly related to the species of Sinosenecio, some of which may belong to the typical subtribe Tussilagininae and others may belong to subtribe Tephroseridinae (Wang et al., 2009; Liu and Yang, un- publ.). The nearest likely relatives of Hainanecio within subtribe Senecioninae could not be determined with cer- tainty in our analysis, which indicates that H. hainanensis shows no close affinities with any genera sampled. Hain- anecio may better be regarded as a fairly isolated member of the subtribe until further systematic data are available to elucidate its affinities. Several lines of evidence (morphological, palyno- logical, cytological, and molecular), therefore, strongly support the segregation of Hainanecio hainanensis as a distinct genus. Hainanecio is easily distinguished from Sinosenecio through a series of characters as given in Table 1. Hainanecio Y. Liu & Q. E. Yang, gen. nov.—TYPE: Sene- cio hainanensis Chang & Tseng in Fl. Hainan. 3: 585. 1974.