Didymocarpus lobulatus (Gesneriaceae), a new species from Zhejiang Province, East China

Abstract Didymocarpus lobulatus, a new species endemic to Zhejiang province, eastern China, is described and illustrated with photographs. The new species is morphologically similar to D. heucherifolius, D. cortusifolius and D. salviiflorus in leaf morphology, but can be easily distinguished by a combination of characters, including the shape of bracts, calyx and calyx lobes.


Introduction
The delimitation of Didymocarpus has varied considerably over time with recent results from both molecular phylogenetic studies and morphological revisions , Möller and Clark 2013, Li et al. 2016. Now, prior to the new species being described here, there are approximately 70 species in the world  consisting of 34 species and four varieties in China (Cai et al. 2016).
Didymocarpus Wall. (Gesneriaceae) was once considered to consist of about 180 species (Wang et al. 1998). However, it was split into three genera: Didymocarpus s.s., Henckelia Spreng., and Hovanella A.Weber & B.L.Burtt (Weber and Burtt 1997). Thus, Didymocarpus was left with about 70 species after the removal of the Madagascan, southern Indian and Sri Lankan and most Malesian species (Nangngam and Maxwell 2013). Didymocarpus sensu stricto currently contains 70 species . According to the treatment of Didymocarpus s.l. in Flora of China (Wang et al. 1990(Wang et al. , 1998, this genus was recognised and divided into two sections: sect. Didymocarpus (herbs with stems (0.7-)3-62 cm long) and sect. Heteroboea (herbs stemless).  Li & F.S. Wang, (2015). The other section, sect. Heteroboea, includes seven species and one variety and is endemic to South and East China (Wang et al. 1990(Wang et al. , 1998Li and Wang 2004). In the past five years, two new taxa were discovered and published in eastern and southern China, namely Didymocarpus heucherifolius var. yinzhengii J.M. Li & S.J. Li (2014) from Hunan province and D. dissectus Fang Wen, Y.L. Qiu, Jie Huang & Y.G. Wei, (2013) from Fujian province.
In 2010, one of the authors (HX) found an unknown Didymocarpus species with the previous year's fruits during field investigations in Zhejiang Province, China. Soon afterwards, the same species was again collected by the other authors (XWY & ZJJ) during floristic surveys in 2014. Based on the recollected specimens of this uncertain species and from detailed inspection in 2016 and 2017, we confirmed it belongs to Didymocarpus because of its disc-like stigma (Wang et al. 1998) and it is a member of sect. Heteroboea as it is a stemless herb. We also concluded that this plant is new to science after thoroughly consulting the related literature (Wang et al. 1990, Wang et al. 1998, Li and Wang 2004. Here, the new species is described and illustrated and its morphological characters are compared with its morphologically similar congeners.

Material and methods
Measurements and morphological character assessments of the putative new species were undertaken and described using available specimens stored in the following herbaria in China, the United States and the United Kingdom: AHU, E, IBK, KUN, MO, PE and US. In addition, images of other type specimens were obtained from Tropicos (http://www.tropicos.org) and JSTOR Global Plants (http://plants.jstor.org). All morphological characters were studied under dissecting microscopes and are described using the terminology presented by Wang et al. (1998).
Etymology. The specific epithet is derived from the shallowly 5-lobed calyx.

Distribution and habitat.
Didymocarpus lobulatus is locally abundant and endemic to a narrow area in eastern China, surrounding the type locality. This species grows on moist shady cliffs of sandy shale hills, at an elevation of 223 m a.s.l. in type locality. The average temperature is 16.4 °C, the average annual precipitation has been calculated as ca. 1,446.8 mm. The forest is a subtropical monsoon climate evergreen broad-leaved forest. Flowering in May. Another population growing in the Danxia landscape of Chuanyanshijiufeng, Xinchang County, Shaoxing city, not far away from the type locality, was discovered by the first author in 2016. The two places are about 40 kilometres apart.
Proposed conservation status. Based on the present field investigations, Didymocarpus lobulatus is currently only known from two sites around the type locality. The two places are about 40 kilometres apart. The type population, which grew close to a country road, is potentially threatened by human activities. Although no such habitat destruction is currently occurring, this population is likely to be threatened in the foreseeable future under influences of man-made factors, for example, by road widening. Fortunately, the second population has been found in the well-protected core zone of the scenic spot, Chuanyanshijiufeng. Furthermore, this population is healthy and locally abundant with many young plants and seedlings growing in the area. Thus, Map 1. The distribution areas of Didymocarpus lobulatus and its congeners in Zhejiang prov.:  D. lobulatus  D. cortusifolius  D. salviiflorus  D. heucherifolius (in semi-elliptical region, the arrows point).
it seems that this species is not at serious risk now and it is proposed as 'Vulnerable' (VU D2) according to the IUCN Red List Categories and Criteria (IUCN 2016).
Notes. The geographical distributions of Didymocarpus lobulatus and its congeners are identified in Map 1. There are altogether 7 species and one variety of sect. Heteroboea, three species are endemic to East China (Didymocarpus salviiflorus and D. cortusifolius in Zhejiang prov. and D. dissectus in Fujian prov.) and two species and one variety (D. yuenlingensis W.T. Wang, D. sinoprimulinus W.T. Wang and D. heucherifolius var. yinzhengii) endemic to Hunan prov. of South China. Only one species, Didymocarpus heucherifolius, is widespread, being distributed from northern Guangdong prov. of South China, to Jiangxi prov., Fujian prov., Anhui prov. and Zhejiang prov. of East China. As more and more field investigations are undertaken, the biodiversity of sect. Heteroboea in East and South China will be better understood by researchers. The discovery of two new taxa, Didymocarpus dissectus Fang Wen, Y.L. Qiu, Jie Huang & Y.G. Wei (2013) and D. lobulatus, serve as two good examples. Differences between the new species and its morphologically related species in sect. Heteroboea in Zhejiang prov. are shown in the following identification table (Table 1)