Two new species of Allocheilos (Gesneriaceae) from the karst regions in Yunnan, China

Abstract Allocheilos W.T.Wang in Gesneriaceae was described in 1983 and is characterized by its 4-lobed adaxial lip and undivided abaxial lip with acute apex. The genus is endemic to the karst regions in southwestern China and is classified as endangered due to habitat loss. During surveys of the karst areas in Yunnan of southwestern China in 2017, we collected two unknown species of the genus and later confirmed their novelty to science based on the detailed observation of their morphological characteristics, viz. A. maguanensis W.H.Chen & Y.M.Shui and A. rubroglandulosus W.H.Chen & Y.M.Shui. Their relationships with the similar species and provisional conservation status are discussed.


Introduction
The genus Allocheilos W.T.Wang in Gesneriaceae is endemic to the karst regions of China and restricted to a shady habitat of limestone hills. The genus shows a stable flower morphology and is characterized by its 4-lobed adaxial corolla lip and undivided abaxial lip (Wang 1983;Wang et al. 1998 (Li 1982;Weitzman et al.1998;Möller et al. 2011;Wang et al. 2011;Chen et al. 2014a, b). However, the latter three exceptions are characterized by the long and narrow corolla tubes, which is different from morphology of flowers in Allocheilos. So far, there are only two recorded species recognized in Allocheilos, which show only weak morphological differences (Wei et al. 2010). They grow on shady rock surfaces of limestone hills in the Dian-Qian-Gui region, viz. Yunnan, Guizhou and Guangxi region in China ( Fig. 1; Fang et al. 1995), and respectively have about 36 individuals of Allocheilos cortusiflorus W.T. Wang (30 in Xingyi,Guizhou and 6 in Luoping) and 40 individuals of A. guangxiensis H.Q.Wen, Y.G. Wei & S.H.Zhong in the field and thus acknowledged as critically endangered (Wang 1983;Wei et al. 2000;Wei et al. 2010).
During surveys in the karst regions in Yunnan in 2016 and 2017 we encountered two unknown species of Allocheilos. At first glance, they look like the species of Petrocodon without flowers in the adjacent region of southeastern Yunnan, such as Pet. viridescens W.H.Chen & Y.M.Shui (Chen et al. 2014a). However, they are characterized by white 4-lobed adaxial corolla lips and short corolla tubes, showing that they are a member of Allocheilos (Figs 2-5). Based on the examination of relevant publications and specimens of Allocheilos from E, IBK, K and P, we found that they are more similar to A. cortusiflorus with short ovary and long style than A. guangxiensis with long ovary and short style (Pellegrin 1930;Wang et al. 1990;Li and Wang 2005;Wei et al. 2010). Furthermore, after the detailed morphological and geographical comparison, we realized that they represent two different species (Table 1). Firstly, there are obvious morphological differences in bracts and staminodes. Secondly, there is a geographical isolation between them, which are respectively distributed in Maguan county and Mengzi county, separated by the Naxi River, SE Yunnan, China (Fig. 1). Thirdly, there are obvious different habitats between them, one of which grows near the summit of the limestone hills and another in the deep limestone sinkholes. So here we described the two species of Allocheilos unknown to science.
Phenology. Flowering is from June to July (in the greenhouse).   Provisional conservation status. Based on observations around the locality, this new species was found in two localities with two minor populations in Maguan Xian, Yunnan province, China. One population grows on limestone cliff around 10 mature individuals, and was easily disturbed by human activities. Another population grows among rocks of the limestone hills with around 20 mature individuals. Thus, further exploration should be conducted while an urgent conservational project is needed for this rare species with extremely small populations (Ma et al. 2013). So far, the species can be provisionally considered as Critically Endangered, CR: B1ab (iii) + 2ab (iii). Discussion. The new species has obvious staminodes, which are usually difficult to observe on specimens in herbaria. So after the detailed observation in the field, the diversity of staminodes will provide us with an opportunity to explore its evolutionary implications for the genus in Gesneriaceae. Diagnosis. The new species is similar to A. maguanensis W.H.Chen & Y.M.Shui with three major staminodes and style longer than ovary, but differs in its elliptic bracts (vs. broadly ovate to rounded), triangular calyx lobes awny at the apex (vs. elliptic and beaked at the apex), and lateral staminodes with red glands (vs. without red glands).
Phenology. Flowering is from October to November (June to July in the greenhouse). Etymology. The epithet refers to the red glands on the top of lateral staminodes, which is an indicator to lead the pollinators to find the nectar. Hitherto, the character was first observed in Gesneriaceae (Weber 2004).
Distribution and ecology. The new species is only distributed in Mengzi county, Yunnan, southwestern China. It grows in deep limestone sinkholes. The adjacent habitat has been disturbed by local people for the purpose of planting corn. The main accompanying plants are Begonia laminariae Irmscher in Begoniaceae, Impatiens apalophylla J.D.Hooker in Balsaminaceae, Pteris deltodon Baker in Pteridiaceae, Thalictrum ichangense Lecoyer ex Oliver in Ranunculaceae.
Provisional conservation status. Based on observations around the locality, this new species was found only in one limestone sinkhole with around 30 mature individuals on the cliffs in three smaller populations. Thus, as the above new species, its further exploration should be conducted while an urgent project is needed for this rare species with extremely small populations (Ma et al. 2013). So far, the species can be provisionally considered as Critically Endangered, CR: B1b (v) + 2b Discussion. At the background of the white flowers, two red glands at the top of staminodes are an important indicator for the pollinators to visit the plants. It is obvious that nectars are hidden at the back of the indicator (Fig. 5C).The discovery will provide us an opportunity to explore the diversity and evolution of staminodes of the genus in Gesneriaceae and the other groups endemic to the karst regions in China and the adjacent countries (Laos, Myanmar, Thailand and Vietnam).