Novelties in Begonia sect. Coelocentrum: B. longgangensis and B. ferox from limestone areas in Guangxi, China

Background The spectacular karst limestone landscape in Guangxi harbors high-level diversity and endemism of Begonia species, especially those of sect. Coelocentrum. In continuation of our studies in this area, we report the discovery of two attractive new species from southwestern Guangxi: Begonia longgangensis and B. ferox. Results Begonia longgangensis resembles B. liuyanii, also from Longgang Nature Reserve, in the broadly ovate to suborbicular leaf blade, differing by the much smaller leaves, subglabrous leaf surface, pink flowers, dichasial cymes and the remarkably long stolons sent out from rhizomes. Unexpectedly, both diploid (2n = 30) and triploid counts (2n = 45) were observed in plants collected from the type locality. Begonia ferox probably has the most prominent bullate leaves for the genus. In this aspect, it is similar to B. nahangensis reported from northern Vietnam recently, but is readily distinguishable by the ovate, chartaceous leaves with an acuminate apex; tomentose peduncle not exceeding petioles; and the much larger stature in vegetative parts. A diploid count of 2n = 30 was determined for this unique new species. Conclusions All available data support the recognition of the two new species. Begonia longgangensis has remarkably long stolons and B. ferox is characterized by the prominent bullate leaves. Line drawings, color plates and comparisons are provided to aid in identification of the novelties. Electronic supplementary material The online version of this article (doi:10.1186/1999-3110-54-44) contains supplementary material, which is available to authorized users.


Background
The area from South China to North Vietnam harbors very high levels of biological diversity (Sodhi et al., 2004). Inventorying the biological diversity in this region, however, is largely insufficient (Hou et al., 2010). Numerous new taxa have been described from there in recent years, especially from the limestone areas, e.g. Aspidistra: Hou et al., 2009, Lin et al., 2010, Liu et al., 2011, 2013Begonia: Fang et al., 2006, 2008, Liu et al., 2005, Peng et al., 2005a,b, 2006, 2008a,b, 2010Primulina: Xu et al., 2012, 2013Oreocharis: Liu et al., 2012;Polystichum: He and Zhang 2011, Zhang and He, 2009a,b, Zhang et al., 2010 In continuation of our studies of Chinese Begonia, we report the discovery of two additional new species, B. longgangensis and B. ferox, from limestone karsts in southwestern Guangxi.
All 19 species of Begonia sect. Coelocentrum that we studied cytologically uniformly had the chromosome number of 2n = 30 , of which seven

Ecology and distribution
Stoloniferous herb on jagged limestone rocks in evergreen broadleaf forest; known only from the type locality in Longzhou County, Longgang Nature Reserve, Guangxi, China (Figure 4).

Phenology
Flowering from March to June; fruiting from May to August.

Etymology
The specific epithet is derived from the type locality, Longgang Nature Reserve, Guangxi.

Chromosome cytology
Somatic chromosomes at metaphase of Begonia ferox were determined to be 2n = 30 (Figure 7). The chromosome complement of the new species showed a bimodal variation in length. Among the 30 chromosomes, two were longer, ca. 1.8-1.9 μm long (Figure 7: arrows), and the rest of 28 were shorter, ca. 0.7-1.4 μm. The two longest chromosomes were clearly metacentric, however, the centromere positions of most chromosomes could not be determined. Satellites were not observed. All 20 taxa, including B. longgangensis, of Begonia in sect. Coelocentrum that were studied cytologically showed the single chromosome number of 2n = 30 (Legro and Doorenbos, 1969;Peng et al., 2012)

Ecology and distribution
Known only from the type locality in southwestern Guangxi, China (Figure 4). On limestone rocks with abundant leaf litter or on bare rocky slopes in evergreen broadleaf forest, very rare.

Etymology
The specific epithet is derived from the fierce-looking leaves with very prominent bullae.

Notes
Begonia ferox resembles B. nahangensis from Vietnam (Averyanov and Nguyen, 2012) in the bullate leaves, differing by the ovate, chartaceous leaves with an acuminate apex; tomentose peduncle not exceeding petioles; and the much larger stature in most vegetative parts. Detailed comparison of the two species is provided in  Outer tepals light olive-green, broadly reniform, 0.5-0.6 cm long, 0.9-1.1 cm wide; inner 1 narrowly obovate, 0.5-0.6 cm long, 0.3-0.35 cm wide