﻿ Sinoseneciominshanicus (Asteraceae, Senecioneae), a new species from south-eastern Gansu and northern Sichuan, China

﻿Abstract Sinoseneciominshanicus (Asteraceae, Senecioneae), a new species from south-eastern Gansu (Wenxian and Zhugqu counties) and northern Sichuan (Pingwu county), China, is described and illustrated. This species is similar to S.rotundifolius, a species locally endemic to Songpan county in northern Sichuan, in having a scapigerous habit, orbicular leaves and solitary capitula, but differs by the presence (vs. absence) of stolons and by having thinner rhizomes (ca. 2 mm vs. more than 5 mm in diameter), stems proximally sparsely fulvous arachnoid or glabrescent (vs. densely sericeous-villous) and obscure (vs. conspicuous) main veins on adaxial surface of leaves. The chromosome number of the new species is reported to be 2n = 60. Colour photographs of living plants in the wild and a distribution map are provided for the new species and S.rotundifolius. The geographical distribution of S.rotundifolius is also corrected, with the previous record of this species from south-eastern Gansu (Wenxian county) actually referring to S.minshanicus.


Introduction
During a botanical trip in 2016 in connection with the biodiversity survey of the Xuebaoding National Nature Reserve in Pingwu county in northern Sichuan province, China, we discovered an unusual population of Sinosenecio B. Nord. (Asteraceae, Senecioneae) (Figs 1-3). At first glance, the plants most closely resemble those of S. rotundifolius Y.L. Chen in having a scapigerous habit, orbicular leaves and solitary capitula, but are distinguishable immediately by having long and slender stolons (Figs 1E,2A,B and 3). Closer examination revealed that the population in question is distinct from S. rotundifolius also by having thinner rhizomes (ca. 2 mm vs. more than 5 mm in diameter), stems proximally sparsely fulvous arachnoid or glabrescent (vs. densely sericeous-villous) and obscure (vs. conspicuous) main veins on adaxial surface of leaves (Figs 1E,2D,4,5E and F). Moreover, the plants of the population prefer shaded and moist habitats on rocky cliffs and slopes along stream sides , while S. rotundifolius has been found only amongst Betula or Rosa bushes on arid slopes (Fig. 5A). During a botanical trip to Zhugqu county in south-eastern Gansu province in 2022, we discovered a population of Sinosenecio with the same morphological characters and habitats (Figs 6-7) as the population in northern Sichuan. We therefore determined that these two populations represent a hitherto undescribed species. Our re-examination of two collections identified on the determination slips or cited as S. rotundifolius by Liu (2010), Baishuijiang Exped. 0320 (PE; http://www.cvh. ac.cn/spms/detail.php?id=eaffdad4) and Baishuijiang Exped. 0800 (PE; http://www. cvh.ac.cn/spms/detail.php?id=eaffdb62), from Wenxian county in south-eastern Gansu revealed that they also belong to this new species. This species is described below and its somatic chromosome number (2n) is also reported.  Fig. 3.

Sinosenecio minshanicus
Diagnosis. Sinosenecio minshanicus most closely resembles S. rotundifolius in having a scapigerous habit, orbicular leaves and solitary capitula, but differs by the presence (vs. absence) of stolons and by having thinner rhizomes (ca. 2 mm vs. more than 5 mm in diameter), stems proximally sparsely fulvous arachnoid or glabrescent (vs. densely sericeous-villous) and obscure (vs. conspicuous) main veins on adaxial surface of leaves.
Phenology. Flowering in June; fruiting in July. Etymology. The specific epithet, "minshanicus", is derived from Min Shan, a chain of mountains extending from south-western Gansu to northern Sichuan, China. The currently known localities of the new species are all situated in the Minshan Mountains region.  Distribution. Sinosenecio minshanicus is currently known from south-eastern Gansu (Wenxian and Zhugqu counties) and northern Sichuan (Pingwu county), China (Fig. 10). It grows on shaded and moist places in forests or on rocky cliffs and slopes along stream sides at altitudes of 2200-3000 m above sea level.   Conservation status. Sinosenecio minshanicus is currently known from Wenxian and Zhugqu counties in south-eastern Gansu and Pingwu county in northern Sichuan, China. Only approximately 30 to 50 mature individuals were discovered each in the Pingwu and Zhugqu populations. They are scattered within ca. 1 km along a valley. Data of the size of the two Wenxian populations are not available. Although the known populations of S. minshanicus are all located within national nature reserves, some human activities, road building in particular, may destroy their habitats and, thus, severely affect the survival of this species. According to the IUCN Red List Categories and Criteria (IUCN 2012), S. minshanicus may better be categorised as Endangered (EN).
Notes. The genus Sinosenecio as defined by Chen et al. (2011) encompasses two major groups of species, with one having strictly polar anther endothecial cell wall thickenings and base chromosome number of x = 30 and occurring in mountainous areas largely surrounding the Sichuan basin in south-western China and the other having polar and radial thickenings and base chromosome number of x = 24 (rarely 13) and largely occurring in mountainous areas in central and southern China (Liu 2010;Chen et al. 2011;Liu andYang 2011a, b, 2012;Liu et al. 2019;Zou et al. 2020;Chen et al. 2022;Peng et al. 2022;Su et al. 2023). Obviously, S. minshanicus belongs to the first group, in which 15 species are currently recognised, including S. homogyniphyllus (Cumm.) B. Nord., the type species of Sinosenecio and S. rotundifolius, the putative closest ally of S. minshanicus (Liu 2010;Chen et al. 2011;Chen et al. 2022;Su et al. 2023). In this group, S. minshanicus is the only species hitherto known to have slender stolons.
Sinosenecio rotundifolius was described on the basis of a single collection, Inst. Biol. Sichuan Exped. 702 (Fig. 4), from Songpan county in northern Sichuan, China (Chen 1988). It was recorded to be locally endemic to Songpan in the account of Sinosenecio in the "Flora Reipublicae Popularis Sinicae" (Chen 1999). The results of our observation of living plants of this species from the type locality are shown in Fig. 5. As mentioned earlier, Liu (2010) cited two collections, Baishuijiang Exped. 0320 (PE) and Baishuijiang Exped. 0800 (PE), from Wenxian county in south-eastern Gansu under S. rotundifolius, thus extending the distributional range of this species. This treatment was adopted by Chen et al. (2011) in the account of Sinosenecio in the "Flora of China". We re-examined these two collections and found that they have slender stolons and match S. minshanicus well also in other characters and thus belong to this species. The previous record of S. rotundifolius from south-eastern Gansu actually refers to S. minshanicus. Currently S. rotundifolius is indeed known only from its type locality in Songpan county in northern Sichuan, not occurring in south-eastern Gansu. As pointed out by Jeffrey and Chen (1984), Sinosenecio is noteworthy for the narrow endemism of many of its species.
Sinosenecio minshanicus occurs in the same valley together with another species of the same group in the genus, i.e. S. pingwuensis Xiu J. Su et al. (Su et al. 2023). Both of them prefer shaded and moist microhabitat and share the same flowering time (June). However, we did not observe any morphologically putative hybrids between them, which is probably due to isolation via intrinsic post-zygotic barriers.