Primulina hochiensis var. ochroleuca (Gesneriaceae), a new variety from a limestone area of Guangxi, China, and errata on five new species of Primulina

Abstract Primulina hochiensis var. ochroleuca, a new variety from a limestone hill of karst areas, Guangxi, China is described with color photographs. It resembles P. hochiensis var. hochiensis, P. hochiensis var. ovata and P. hochiensis var. rosulata, but can be easily distinguished by a combination of characteristics, especially by its corolla color. We found only one population with approx. 3000 mature individuals at the type locality. This variety is provisionally assessed as vulnerable [VU C1] using IUCN criteria.


Introduction
By the end of December 2019, the genus Primulina Hance (1883) comprised over 220 species names (infraspecific taxa included) (Wen et al. , 2020IPNI 2020;Tropicos 2020), including many new species published in recent years (e.g., Pan et al. 2020). In all taxa of Primulina in the world at present, 208 were recorded from China and 21 were recorded from Vietnam (Vu 2018;Wen et al. 2020). As the largest genus of Gesneriaceae in China, Primulina s. l. has become representative of the rich diversity in the Chinese Gesneriaceae. Nevertheless, it is still possible to dig deeper into the biodiversity of Primulina (Möller 2019). Those highly diverse taxa mainly grow in limestone areas, which are highly fragmented and heterogeneous (Möller et al. 2016). Most species are micro-endemics with narrow, island-like distributions, often limited to a single cave or karst limestone hill system (Kang et al. 2014). This edaphic complexity may be a strong driver of speciation via habitat specialization (local adaptations) to edaphic microhabitats (Hao et al. 2015). In addition, Kong et al. (2017) suggest that global temperature change is probably the primary driver of diversification in Primulina. And the monsoons and edaphic characteristics are probably also strongly linked to its diversification.
Two amateurs of Gesneriaceae from Guangxi found this unknown taxon in the wild in late September 2017. The population was not in flowering at that time, only the white buds that were about to bloom. They thought it might be a member of P. hochiensis complex because its habit resembles P. hochiensis var. hochiensis and P. hochiensis var. rosulata, but differs from the former by its stolon absent, and from the latter by its conspicuously larger leaf blade and longer pedicel. Although it was thought to be P. hochiensis, some individuals were collected for cultivation. When all the individuals are in flower, they found that all the flowers are yellow and the color is very stable, hence it can be distinguished from all the other varieties by this character. They visited the original locality again in late October 2017 and found all the individuals' flowers are yellow. Some living plants were collected and mailed to GCCC for further study. We grew them in common garden of GCCC with other varieties of P. hochiensis for two years and found that all the flowers of this unknown taxon are yellow, and can be distinguished from all the other varieties. And we made an extensive survey of the surrounding hills in October 2019 when this unknown taxon was in flower. No individual of this unknown taxon was found in the surrounding limestone hills, only some P. hochiensis var. ovata growing on those hills. Though the distribution of this new variety is close to P. hochiensis var. ovata, we can easily tell them apart.
After analyzing the morphological characters on these plants, and comparing them with the other three similar-looking P. hochiensis varieties, we confirmed that it is indeed a new variety of P. hochiensis. Thus, we describe it here. Diagnosis. The new variety can be easily distinguished from all varieties of Primulina hochiensis by its pale yellow corolla. It differs from the typical variety, P. hochiensis var. hochiensis by its stolon lacking and obviously longer petiole (5-7 cm long); from P. hochiensis var. ovata by its stolon lacking, obviously longer petiole (5-7 cm long) and longer pedicel (1.5-2 cm long); from P. hochiensis var. rosulata by its longer pedicel (1.5-2 cm long), shorter calyx (3.5-4 mm long), corolla throat with one big yellow patch and longer pistil (1.4-1.8 cm long).
Phenology. Flowering occurs from September to November, and fruiting from November to January of the next year.
Distribution and habitat. Primulina hochiensis var. ochroleuca is hitherto only known from the type locality, Xiling Town, Gongcheng County, Guangxi Zhuang Autonomous Region, South China (Fig. 3), and grows on moist and shaded rocky surfaces on the cliff in subtropical evergreen seasonal rain forest.
Preliminary Conservation status. The type population consists of approx. 3000 mature individuals, all growing on moist and shaded rocky surfaces on the cliff. They are easily disturbed by human activities because the distance from the type locality to the local village is short. Parts of vegetation of the type hill have been cleared by local  s.l., 11 Jul 2012, Hui-Ling Liang, Yan-Cai Shi & De-Xin Kong, 120711 (IBK!).