﻿Sinoseneciopingwuensis (Asteraceae, Senecioneae), a new species from northern Sichuan, China

﻿Abstract Sinoseneciopingwuensis (Asteraceae, Senecioneae), a new species from Pingwu county in northern Sichuan, China, is described and illustrated. This species is distinguished in Sinosenecio by having leathery, glabrous, ovate or ovate-oblong leaves often pinnately-veined and solitary capitula 2.3–4.3 cm in diameter, a unique character combination hitherto never recorded in the genus. Two floral micromorphological characters (configuration of filament collar of stamens and anther endothecial cell wall thickenings) and achene surface features of the new species are reported. Color photographs of living plants and a distribution map are also provided for the new species.


Taxonomic treatment
Floral micromorphological characters and achene surface features. The filament collar of stamens in Sinosenecio pingwuensis consists of uniformly-sized cells ( Fig. 4A) and the anther endothecial cell wall thickenings are strictly polar (Fig. 4B). The achene is glabrous and smooth (Fig. 4C).
Phenology. Flowering in June; fruiting in July.  Etymology. The specific epithet, "pingwuensis", refers to the type locality of the new species, i.e. Pingwu county in northern Sichuan, China.
Distribution and habitat. Sinosenecio pingwuensis is currently known only from its type locality, i.e. Pingwu county in northern Sichuan, China (Fig. 5). It grows on moist rocky cliffs along stream sides in a valley at an altitude of ca. 2300 m above sea level.
Conservation status. The currently only known population of Sinosenecio pingwuensis at the type locality comprises ca. 80 individuals growing on rocky cliffs. They are scattered within ca. 1 km along a valley. Although the population is located in the Xuebaoding National Nature Reserve, some human activities, road building in particular, may destroy the habitat of the population and, thus, severely affect the survival of this species. According to the IUCN Red List Categories and Criteria (IUCN 2012), the new species should be categorised as Critically Endangered (CR).
Notes. The genus Sinosenecio, as defined by Chen et al. (2011), comprises two major species assemblages with different configurations of anther endothecial cell wall thickenings (polar and radial vs. strictly polar), different base chromosome numbers (x = 24, rarely 13 vs. x = 30) and different geographical distributions (central and southern China vs. areas largely surrounding the Sichuan basin in south-western China) (Liu 2010;Liu andYang 2011a, b, 2012;Liu et al. 2019;Zou et al. 2020;Chen et al. 2022;Peng et al. 2022). Judging from its strictly polar anther endothecial cell wall thickenings and its occurrence only in Pingwu county at the northern margin of the Sichuan basin, S. pingwuensis should belong to the latter assemblage, in which 14 species are currently recognised, including S. homogyniphyllus (Cumm.) B. Nord., the type species of Sinosenecio (Liu 2010;Chen et al. 2011;Chen et al. 2022). Regrettably, we have been unable to check the chromosome number of S. pingwuensis due to our failure in transplanting living plants to obtain actively growing roots for squashing. From its configuration of strictly polar anther endothecial cell wall thickenings, S. pingwuensis should have a somatic chromosome number (2n), based on x = 30, very likely 2n = 60, the commonest somatic chromosome number in this assemblage (Liu and Yang 2011a). In Sinosenecio, the strictly polar anther endothecial cell wall thickenings correlate well with the base chromosome number of x = 30 (Liu 2010;Liu and Yang 2011a, b).
In the same valley where Sinosenecio pingwuensis occurs, we discovered another hitherto undescribed species of Sinosenecio. This species and S. pingwuensis should belong to the same species assemblage of the genus. Both prefer shaded and moist microhabitat and grow on rocky cliffs. Although they do not grow strictly in the same community, some individuals of them are less than 100 m away from each other and they begin to flower at the same time (in June). We did not observe, however, any morphologically putative hybrids between them. This is probably due to isolation via intrinsic post-zygotic barriers. We will report this undescribed species elsewhere.