﻿Primulinapingnanensis, a new species of Gesneriaceae from Guangxi, China

﻿Abstract A new species of Primulina, P.pingnanensis, from the Guangxi Zhuangzu Autonomous Region, China, is described and illustrated here. It is morphologically similar to P.orthandra but has significant differences in the bracts, corolla tube and lobes shape, as well as in the indumentum of the outer surface of the corolla, the filaments, the staminodes and the anthers. Colorful photographs and essential information of this new taxon are also provided, including detailed taxonomic description, distribution, habitat, the comparison table, and the IUCN conservation status. We also discuss a validation of new combination P.crassifolia and Chiritacrassifolia.


Introduction
As of December 2022, about 250 taxa (including varieties) of Primulina Hance had been published worldwide, with 215 species and 18 varieties distributed in China and 18 species in Vietnam (GRC 2022; Wei et al. 2022). Based on the quantity and distribution of the Primulina species, it is apparent that the Karst limestone areas in Guangxi, China, are the center of Primulina diversity and distribution (Hao et al. 2014;Kong et al. 2017;Wei 2018;Li et al. 2019;Xu et al. 2019). This further indicates that more undescribed Primulina species may still be found in the Karst ecosystem of South and Southwest China (Möller 2019), especially in karst caves (Xin et al. 2018;Fu et al. 2022), cliffs and gorges. Averyanov et al. (2020) described a new species of Chirita in North Vietnam, which they named Chirita crassifolia Aver. & K.S.Nguyen. In 2022, after verification, Möller and collaborators transferred C. crassifolia to Primulina as P. crassifolia (Anh et al. 2022). Primulina crassifolia (Aver. & K.S.Nguyen) T.T.P. Anh, F. Wen & Mich.Möller, comb. nov. Basionym: Chirita crassifolia Aver. & K.S.Nguyen, Pl. Diversity Fl. Veg. Bat Dai Son 254 (2021). We emphatically revise the Latin name from 'Chirita crassifolia' to 'Primulina crassifolia' here and provide appropriate notes.
In March 2018, when we were on an expedition in Pingnan County, Guangxi, China, we found an unknown Primulina-like plant growing at the crevices of rocks on the top of a limestone cliff. According to its leaf arrangement (rosette), fleshy leaves, tubular corolla, and cracked fruits (capsule with parietal placentation), it should be included in Primulina. However, it did not match any known species of this genus. In addition, this species distinguishes from the genus Petrocodon by its lingulate stigma, curved filaments, and fleshy leaves. We collected specimens in the field and introduced some living plants into cultivation at the nursery of the National Gesneriaceae Germplasm Resources Bank of GXIB and the Gesneriad Conservation Center of China. The morphology of the cultivated plants has not changed from that of the wild plants during the past three years. We compared the collected specimens and living plants with other known type specimens and living plants of Primulina, and we found that it is distinctly different from other species of Primulina, especially those distributed in Guangxi and recently published species of Primulina (e.g., Du et al. 2021;Xiong et al. 2022;Pan et al. 2022), which are also different from this new taxon. We then confirmed that it was a new species.

Material and method
The description is based on specimens collected in the wild. The measurements and morphological characteristics of the new species were taken from the type specimens processed by the authors. The type specimens of the new species were deposited in IBK. We examined Primulina specimens in IBSC, K, IBK, KUN, US, PE, and VNMN. We also searched two online herbaria, Chinese Virtual Herbarium (CVH, http://www.cvh.ac.cn) and Chinese Field Herbarium (CFH, http://www.cfh.ac.cn), to find species with similar morphology. We determined it to be an undescribed taxon. All morphological characters were studied under a dissecting microscope and were described using the terminology used by Wang et al. (1990Wang et al. ( , 1998.
Phenology. Flowering from the second half of March to the first half of April, fruiting from June to July.
Etymology. The specific epithet is derived from the type locality, Pingnan County. This county is the birthplace of Mr. Chou's mother. Thus, Mr. Chou strongly suggested using "pingnanensis" as the scientific name. Vernacular name. Píng Nán Bào Chūn Jù Tái (Chinese pronunciation); 平南 报春苣苔 (Chinese name).
Distribution and habitat. Primulina pingnanensis is only known from the type locality, Shuangma Village, Pingnan County, Guigang City, Guangxi Zhuangzu Autonomous Region, growing on limestone cliffs at an elevation of ca. 50 m. The average temperature in the distribution area is 22.6 °C, while the average annual precipitation is 1050-2100 mm. The habitat is very close to the village with human activities.  Preliminary conservation assessment. The terrain in the North and South of Pingnan County is mountainous, while the central area is flat. Very few limestone hills are in the plains, but some mountains are near Shuangma Village. After finding the new species, we conducted several detailed explorations of the area. The current survey results showed that this species has a small population at the top of a limestone mountain near Shuangma Village, with fewer than 200 individuals. According to the results of our field investigations in the type locality and adjacent regions, the EOO and AOO of Primulina pingnanensis are about 2 km 2 and 0.1 km 2 , respectively. The severe drought in the second half of 2022 has seriously affected the population. According to the field survey, it is preliminarily estimated that the number of individuals in this population has decreased by 40% or more. More in-depth habitat surveys are warranted to determine if there are more populations nearby. For this current study, we temporarily assess the status of this species as Critically Endangered [CR B1+B2ab (iii,v)], according to the IUCN Red List Categories and Criteria (IUCN 2022).

Validation of new combination in Primulina
When the new combination for Primulina crassifolia was made by Anh et al. (2022), it was later noticed that the combination was invalid. Therefore, we validate it here.

Discussion
The Karst and Danxia landforms from south & southwest China to the north Indo-China Peninsula are well-known for their high species diversity and endemism levels. Some interesting genera of Gesneriaceae for example, Primulina, Petrocodon Hance, and Hemiboea Clarke have been attracting the attention of botanists and taxonomists in the past decades. Primulina speciation is positively associated with changes in past temperatures and East Asian monsoons. Climatic change around the mid-Miocene triggered an early burst (Kong et al. 2017;Xu et al. 2019;Hsieh et al. 2022). There is abundant diversity in the morphology of the vegetative and reproductive organs of Primulina. Still, it can be distinguished by its rosette leaves, tubular corolla, parietal placentation, etc. We concluded that P. pingnanensis is an undescribed species of Primulina based on extensive investigation in south and southwest China. A comparison of known live plants and specimens of the genus Primulina. P. orthandra can be regarded as similar to P. pingnanensis because they both have similar leaf morphology, calyx, and purple corolla. However, the differing characteristics of the peduncle, bract, stamen, and staminodes can quickly distinguish the two species from each other. The high species diversity and restricted distributions on limestone habitats have made the calciphilous Primulina an ideal study subject for understanding plant radiation on Sino-Vietnamese limestone karsts ). The habitat of P. pingnanensis is located in the mountains in the middle of Pingnan County. The rest of the area is a flat plain. The spatial heterogeneity has created a unique species of Primulina in Pingnan. This suggests that the karst areas in southern China have acted as both "museums" and "cradles" of plant evolution (Xu et al. 2019). The discovery and publication of this new species supplements the diversity of Primulina distributed in Guangxi. It further indicates that there are more undiscovered new species of Primulina in the vast karst areas of south China (Hong et al. 2020;Fu et al. 2022).