Primulinasilaniae sp. nov. (Gesneriaceae) from the limestone area of Guizhou Province, China

Abstract Primulinasilaniae X.X.Bai & F.Wen, a new species of Primulina Hance (Gesneriaceae) from the limestone area of Wangmo County, Guizhou Province, is described and illustrated. The new species is similar to P.spiradiclioides Z.B.Xin & F.Wen, but can be easily distinguished from the latter by a combination of characteristics, especially in the lateral veins of its leaf and floral shape and tube. At present, three populations in one locality of this new taxon were found, totaling about 600 mature individuals. According to the IUCN Red List Categories and Criteria (Version 3.1), the species is provisionally assessed as Vulnerable [VU D1].


Introduction
Hance, a British botanist and the Vice Consul for Foreign Affairs of Huangpu Port in Guangdong (Hance 1883). The type species of this genus is P. tabacum Hance, which once was considered a rare cave plant in limestone montane areas and collected in Lianzhou City, Guangdong Province, China (Wang et al. 2013). After 2011, plant taxonomists revised the classification system of Chirita and its related genera based on molecular and morphological evidence. Now, as a result of this reorganization and newly described species, the newly defined Primulina has become the most diverse genus of Gesneriaceae in China (Li and Wang 2007;Möller et al. 2009Möller et al. , 2011Wang et al. 2011;Weber et al. 2011). As of October 2021, there were 219 species (excluding infraspecific taxa) (GRC 2021), and most of the species in this genus were discovered from Guangxi, China (Wei 2018).
Although Primulina has only been found in southern and southwestern China and northern Vietnam, mainly in limestone areas (Möller et al. 2016), there is still great potential to find undescribed species diversity (Möller 2019). As the main locality of differentiation and diversity of Gesneriaceae in China, many new taxa have been discovered or reported in Guizhou (Xu et al. 2017). From 2019 to October 2021, 21 new species (including infraspecific taxa) of the genus Primulina have been described (Wen et al. 2021), including two species from Guizhou Province P. serrulata R.B.Zhang & F.Wen from Rongjiang County (Hong et al. 2019) and P. flexusa F. Wen, Tao Peng & B.Pan (Peng et al. 2020) from Duyun City (Wen et al. 2021).
In July 2020, when we investigated plants in Wangmo County, we found a plant on moist, shady limestone cliffs that appeared to represent an undescribed species of Primulina based on its old fruits and leaves. After regular observation, we photographed the flowers and collected the specimens in November 2020. Comparing these specimens and living plant materials with the type specimens and protologues of all 219 species of Primulina, we found that these specimens and plants neither fit the existing protologues nor conformed to the type specimens of these species. Nevertheless, the shape and texture of leaves are most similar to P. spiradiclioides Z.B.Xin & F.Wen (Xin et al. 2020); it can be distinguished by a combination of several morphological characters of the leaf margin, lateral veins, leaf indumentum, and floral features. Thus, we confirmed that it represented a new species of Primulina and describe and illustrate it here.

Materials and methods
The plant material for description was collected in the field at its type locality in 2020. Morphological observations and dissections of plant material of this new species were made under a stereoscopic microscope (Olympus SZ61, Tokyo, Japan) and measured and described using the terminology used by Wang et al. (1998). Electronic specimens stored in herbaria in China, Vietnam, the United States, and the United Kingdom (e. g. E, GH, HN, IBK, K, IBSC, HITBC, KUN, MO, PE, PH, US, and VNMN) were examined.
Phenology. Flowering from November to February of the following year, fruiting from March to May.
Distribution and habitat. The species has only been found in Wangmo County, the type locality. It grows on moist, shady limestone cliffs at altitudes of 550 to 570 meters.
Provisional IUCN conservation assessment. At present, Primulina silaniae is only found in the type locality. There are three populations with ca. 600 matures individuals, all of which grow on moist and shady limestone cliffs. One of the populations has a small number of mature individuals and is located by the roadside, easily disturbed by human activities. It is therefore assessed as Vulnerable Notes. The leaf of Primulina silaniae is fleshy and brittle, glabrous on both sides, with an entire margint that occasionally has a few long hairs, base tapering to petiole, apex acuminate to obtuse; midrib inconspicuous on adaxial surface, conspicuous on abaxial surface, no lateral veins. These characteristics differ from those of other Primulina species and can be clearly distinguished from Primulina spiradiclioides in morphological characteristics (Table 1).