Synotis panzhouensis (Asteraceae, Senecioneae), a distinct new species with red-purple pappus from southwestern Guizhou, China

Abstract A new species of Asteraceae, Synotis panzhouensis, is described and illustrated from Guizhou Province in China. Compared with other species of the genus, it is distinguishable by having red-purple pappus; additionally, it differs from its closest ally S. nayongensis by the larger involucres and phyllaries, and higher number of phyllaries and disk florets. In addition, detailed discussion of morphological differences, the provisional IUCN status and a distribution map are provided.


Introduction
Synotis (Clarke) C.Jeffrey & Y.L.Chen (Asteraceae, Senecioneae) includes 60 annual and sub-shrubby species predominantly distributed in northern India, Nepal, Bhutan, northern Myanmar, Thailand, Vietnam and southern China (Jeffrey and Chen 1984;Chen 1999;Chen et al. 2011;Tang 2014;Joshi et al. 2013). The genus was separated from Senecio L. mainly due to the anther bases having sterile tailed auricles (vs. without sterile tailed auricles) (Jeffrey and Chen 1984). For China, many taxonomic and nomenclatural novelties within the genus have been reported in recent years (Tang et al. 2013a(Tang et al. , b, c, 2014Tong et al. 2017;Li et al. 2018), and at the present time, approximately 50 species are recorded in China, of which 24 are endemic (Tang 2014, Tang unpublished data).
During an expedition to Panzhou, Guizhou Province, China in 2020, we found an unusual population of Synotis at pre-anthesis. Initially, the plants seemed to be similar to S. nayongensis C.Jeffrey & Y.L.Chen, but further examination revealed several diagnostic differences between the Guizhou population and S. nayongensis; therefore, we describe the Guizhou plants as a new species to science here.
Distribution. Synotis panzhouensis is endemic to southwestern Guizhou, China (Fig. 4); to date, only known from the type population.
Habitat. Growing in mixed forest with other herbs in limestone mountains at an elevation of ~1800 m.
Phenology. Flowering from late August to September; fruiting October. Etymology. The specific epithet is derived from Panzhou, the type locality of the species. The Chinese name is '盘州合耳菊 (Pan zhou he er ju)'.
Discussion. As shown in Figs 1-3, Synotis panzhouensis is similar to S. nayongensis in the oblanceolate or obovate rosulate leaves at the base of synflorescence, the narrow paniculoid thyrse and absence of ray florets. However, we detected significant differences between the two species as listed in Table 1.
Synotis panzhouensis is only distributed in Panzhou, southwestern Guizhou, China, while S. nayongensis is mainly distributed around northwestern Guizhou (Ruan et al. 2020), with its type locality in Nayong, a county located 200 km NE from Panzhou. From all other species of Synotis, S. panzhouensis is very distinct in the red-purple pappus. According to our observation of the plants in vivo, as well as a critical examination of taxa throughout the genus, most species (~50 spp.) have white pappus. Five species in sect. S. ser. Fulvipapposae C.Jeffrey & Y.L.Chen often have white or stramineous pappus, which is consistent with the descriptions reported by Jeffrey and Chen (1984), Chen (1999) and Chen et al. (2011). The pappus colour of S. vaniotii (Lévl.) C.Jeffrey & Y.L.Chen and S. palmatisecta Y.L.Chen & D.J.Liu were described as rubescent, but this might be the result of inattentive observation, for both of the species were found with white, or rarely pale brown pappus during our field and herbarium observations. It is noteworthy to mention that S. chenopodiifolia (DC.) M.Tang, C.Ren & Q.E.Yang, a species always reported with brown or yellow pappus, has been reported with a dark purple pappus in a population in Gyirong County (Tang et al.   2014), but such variation is rather atypical in the species. Synotis chenopodiifolia is a plant to 80-180 cm with triangular-ovate or triangular-hastate leaves and a capitulum with 5 phyllaries, 2 or 3(-4) disk florets, and it obviously differs from the leaf characters and capitulum characters as seen in S. panzhouensis. Morphologically, following the characters and delimitation of Jeffrey and Chen (1984) and Tang (2014), S. panzhouensis is best referred to Synotis sect. Synotis ser. Synotis due to the leaves gathered at the apex of the vegetative stem and its terminal inflorescence.
IUCN Red List Category. Synotis panzhouensis was found in a single location with an extremely small population in Panzhou, southwestern Guizhou, China. Due to the remote distance and difficult and dangerous accessibility to the type locality, the population was not disturbed by human activity and currently appears to be growing very well. However, according to our observation, the population comprises no more than 100 plants, and with a small geographical range of no more than 1000 m 2 , we recommend that S. panzhouensis be categorized as Critically Endangered (CR) using criteria B and C following the IUCN Red List categories (IUCN 2019).