Oreocharis flavovirens, a new species of Gesneriaceae from Southern Gansu Province, China

Abstract Oreocharis flavovirens is a new species of Gesneriaceae from Gansu, China and is described and illustrated here. It is morphologically similar to O. glandulosa, O. humilis and O. farreri, but those congeners of this new taxon can be distinguished by several salient characters. A description of O. flavovirens, together with illustrations and photos, are presented.


Introduction
In the summer of 2018, two of the authors (QWH and GYF) encountered an unknown Gesneriaceae species with young flowers during a botanical survey in Gansu Province. Subsequently, the plants were monitored in the field and flowering speci-mens were collected in autumn. The gross morphology, such as leaves in a basal rosette with spiral leaf arrangement, shape of the corolla and pistil, including stigma, indicates that this taxon can be assigned to Oreocharis Benth., which now includes species from eleven former genera (Möller et al. 2011(Möller et al. , 2014(Möller et al. , 2015. Many new taxa of this genus have been discovered and published in recent years (e.g. Cai et al. 2017, Chen et al. 2016, 2017a,b, 2018, Do et al. 2017, Guo et al. 2018, Li et al. 2017, Yang et al. 2017. After thorough comparisons of diagnostic morphological and anatomical features of similar taxa from China, Vietnam and Thailand (Pan 1987, Wang et al. 1998, Li and Wang 2005, Wei et al. 2010) and herbarium specimens also being consulted, it was concluded that it was a species new to science and thus described and illustrated here.

Oreocharis flavovirens
Etymology. The specific epithet is derived from its greenish-yellow corolla.

Distribution and habitat.
To date, Oreocharis flavovirens is only found at the type locality, Yuhe Provincial Nature Reserve, Gansu Province, which is located at the intersection of the Qinling Mountains and the Minshan Mountains. This species grows amongst moss on moist shady surfaces of stones near waterfalls, at an elevation of 950-1200 m a.s.l. The average temperature is 21°C, the average annual precipitation has been calculated as ca. 780 mm. The forest is a subtropical evergreen broad-leaved forest.
Notes. As is known, Oreocharis Benth. is a genus (more than 120 species) in the angiosperm family Gesneriaceae, which are mainly distributed in southern and southwestern China, at the same time with a few species extending into Vietnam, Myanmar, India, Bhutan, Japan and Thailand (Cai et al. 2017. SW China is rich in species diversity of the genus in China, especially on the north-facing shady slope nearby the summit of southern Yunnan Province and most species occur in relatively restricted and geographically isolated localities with very few widely distributed (Li and Wang 2005, Wei et al. 2010, Möller et al. 2011 Fig. 3], which grows at low elevations on rather cool rocks or very steep banks of cool clammy soil that grows a fine film of moss in S. Gansu Province (Craib 1920 Fig. 5], growing on shady and damp rocks in montane regions of Sichuan Province (Hooker 1890). No new species of Oreocharis were described from between the early 19 th and late 20 th Century in the regions, the new findings complementing the species richness of the genus in Central China. Due to the high endemism in the genus (Chen et al. 2017b(Chen et al. , 2018, Table 1 details the differences between these species growing in the same regions.
Obviously, the genus is special for its remarkable floral diversity and it has made this genus to be one of the most taxonomy-difficult groups in the family. The new species, Oreocharis flavovirens which has a light-yellow cylindrical corolla with a distinct upturned tube, is a good example. The shape of the corolla tube, cylindrical and upturned, is a distinct character that not many species in Oreocharis possess. If we only consider the similarity of corolla tube shape, it is close to Oreocharis tubiflora K.Y. Pan and O. argyreia Chun ex K.Y. Pan, including constriction at the mouth but the latter two are lacking the upturned corolla tube. Given the corolla shape, the corolla of several species of former Ancylostemon Craib are similar too, except the tubes are straight or slightly turned down, but not up, though the flowers are predominantly yellow (rarely pink in A. ronganensis K. Y. Pan=Oreocharis ronganensis (K.Y.Pan) Mich.     Möller & A.Weber), only here the tubes of previous Opithandra are slightly more trumpet-shaped in dark pink or pink and have two fertile stamens rather than four (Wang et al. 1998, Li and Wang 2005, Wei et al. 2010. All in all, the upturned corolla tube combined with its greenish-yellow colour could be used alone to differentiate the new species from others in the genus. Furthermore, although the genus Oreocharis was redefined to accommodate species with distinctive floral morphologies from ten other genera, based on molecular phylogenetic studies in the last two decades, the evolutionary trends of the floral characters have not yet been understood comprehensively. The major causes of the incongruence and conflict between classical taxonomy and molecular phylogenetic studies for Oreocharis s.l. remain largely unexplored. There are other similar examples in Gesneriaceae of Asian, for example, Primulina s.l. (Wang et al. 2011, Weber et al. 2011a and Petrocodon s.l. (Weber et al. 2011b, Lu et al. 2017. Additional specimens examined (paratypes). Gansu Province: Yuhe Provincial Nature Reserve, Longnan City, 24 September 2019, in fruit, Yun-Feng Gao et al.: WF19092401 (AHU).