Camellia debaoensis (Theaceae), a new species of yellow camellia from limestone karsts in southwestern China

Abstract Camellia debaoensis R.C.Hu & Y.Q.Liufu, sp. nov. is described and illustrated as a new species from southwestern Guangxi, China. It is morphologically similar to Camellia pubipetala Y. Wan & S. Z. Huang, C. mingii S.X. Yang and C. tuyenquangensis D.V. Luong, N.N.H. Le & N. Tran, but it differs from these species in having glabrous young branches, glabrous petiole, glabrous sepals, glabrous petals, glabrous stamens and glabrous ovary, 10 petals, cylindrical ovary and style 3-lobed to 1/6 style length.


Introduction
Guangxi Zhuang Autonomous Region of southern China is an area noted for its karst landscapes (Hou et al. 2010). The limestone region in southwestern Guangxi harbors very high levels of biological diversity and is recognized as one of 20 centers of plant endemism in China (Myers et al. 2000, López-Pujol et al. 2011. Yellow camellia, a subgroup of Camellia (Theaceae), are characterized by yellow, waxy and shiny petals (Chang and Ren 1998). Because of their beautiful flowers and useful chemical constituents, yellow camellias have considerable economic value in breeding, as well as traditional Chinese medicine and commercial tea production (He et al. 2016). Before 2007, fewer than 20 yellow camellias from China were recognized, according to the literatures (Ye and Xu 1992;Chang and Ren 1998;Min 2000;Min and Bruce 2007). Most of them are only distributed in southwestern Guangxi, which had been considered as a center of diversity of the yellow camellia. In recent years, many new species of yellow camellia have been reported from northern Vietnam and southern China (e.g. Tran and Nguyet 2005;Orel 2006;Orel andWilson 2010, 2012;Orel et al. , 2013Orel et al. , 2014aTran et al. 2012;Tran and Luong 2013;Huang et al. 2014;Orel and Curry 2015;Tran and Le 2015;Luu et al. 2015;Dung et al. 2016;Luong and Le 2016;Luong et al. 2016a, b;Le et al. 2017;Nguyen et al. 2018;Liu et al. 2019), increasing the total to more than 50 species (Tran et al. 2019) and making northern Vietnam another center of yellow camellia diversity. Generally, yellow camellias are rare and highly endemic due to their small population, narrow distribution and excessive gathering. Recently, almost all Chinese yellow camellia species were categorized as Critically Endangered, Endangered, or Vulnerable species in the Threatened Species List of China's Higher Plants (Qin et al. 2017).
During our floristic survey in limestone karsts of Debao County, southwestern Guangxi, in 2015, we collected several specimens from a population of Camellia with yellow flowers. In the following three years, this population was documented for flowering and fruiting regularly at the same locality. Morphological comparison between the newly collected specimens and other yellow camellias suggested that the specimens from Debao differed from all the previously described species. Therefore, we here describe this material as a new species.

Materials and methods
Several specimens were collected at the entrance of one of the karst caves of Debao County, Jingde Town, Tuoliang village from 2015 to 2018, and were deposited in the herbaria GXMI, IBK, NHMG, KUN. The morpho-photographs of the plants were taken with a Panasonic LX100 camera. This material was confirmed as a new species based on detailed comparison with all other heretofore known yellow camellias, including specimens deposited at PE, KUN, IBSC, IBK, GXMI, HIB, SYS, GXMG, and description from botanical websites (e.g. http://www.cvh.ac.cn/, https://plants. jstor.org/). Herbarium acronyms follow Thiers (2018). The morphological characters were measured using M & G ARL96004. Tran, but it differs from these species in having glabrous young branches, glabrous petiole, glabrous sepals, glabrous petals, glabrous stamens and glabrous ovary, 10 petals, cylindrical ovary and 3-lobed to 1/6 style length.
Phenology. Flowering from December to February of the next year; fruiting from July to August.
Distribution and habitat. Camellia debaoensis grows at the entrance of one of the limestone caves in the karst region of Debao County (Fig. 3)  Etymology. The specific epithet is derived from the type locality, Debao County, Guangxi.
Taxonomic notes. It is noted that there are several classification systems about taxonomic treatments of Camellia, represented by Ye and Xu (1992), Chang and Ren (1998), and Min and Bruce (2007). These systems have different taxonomic opinions on sectional taxonomic treatment of yellow camellias. Considering the inclusiveness of the system of Min and Bruce (2007), the new species should be placed in C. sect. Stereocarpus.    (2007) (Table 1). A key to identifying species of yellow camellia with connate style is provided below. Of these species, the new species is more similar to C. pubipetala, C. mingii, C. tuyenquangensis than to other species by sharing small leaflets, subterminal axillary flowers, 9-13 petals, differentiated bracts, outer filament whorl basally connate, 3-locular ovary, connate style. However, it is well distinguished from these species in having glabrous young branches, glabrous petiole, glabrous sepals, glabrous petals, glabrous stamens and a glabrous ovary (vs. villous in C. pubipetala and C. mingii), 10 petals (vs. 9-13 in C. pubipetala, 12-13 in C. mingii and 12 in C. tuyenquangensis), cylindrical ovary (vs. ovoid in C. mingii and C. tuyenquangensis, spherical in C. pubipetal) and style 3-lobed to 1/6 style length (vs. 3 (or 4)-cleft to 1/3 style length in C. pubipetala, 3-cleft to 1/10 style length in C. mingii, 3-cleft to 1/2 style length in C. tuyenquangensis). The comparisons between C. debaoensis and these species are provided in Table 2. Based on hairs, lamina length, flower size, number of carpels and other characteristics, the new species is also a taxonomic entity distinct from C. oconariana, C. thuongiana, C. luteocerata, C. luteopallida, C. bugiamapensis and C. capitata (Table 1).