Seven new species of Begonia (Begoniaceae) in Northern Vietnam and Southern China

Abstract Since 2016, KIB (Kunming Institute of Botany) and CPC (Centre for Plant Conservation of Vietnam) have conducted several surveys in the transboundary karst regions in Northern Vietnam and Southern China and seven new species in the genus Begonia Linn. (Begoniaceae) are firstly described. Amongst them, two species, Begonia albopunctata Y.M. Shui, W.H. Chen & H.Q. Nguyen and B. erectocarpa H.Q. Nguyen, Y.M. Shui & W.H. Chen, respectively belong to section Sphenanthera with berry fruits and section Leprosae with clavate berry fruits; four species, B. gulongshanensis Y.M. Shui & W. H. Chen, B. minissima H.Q. Nguyen, Y.M. Shui & W.H. Chen, B. mollissima Y.M. Shui, H.Q. Nguyen & W.H. Chen, B. rhytidophylla Y.M. Shui & W.H. Chen, belong to section Coelocentrum with parietal placentation; one species, Begonia bambusetorum H.Q. Nguyen, Y.M. Shui & W.H. Chen, belongs to section Diploclinium with 3-loculed ovary and capsules. The diagnostic characters of these species are described and illustrated in the text and photographs.


Introduction
The Tonkin region is one of the biodiversity hotspots worldwide (Takhtajan 1986;Myers et al. 2000) that include Northern Vietnam and Southern China (Fig. 1). This region is characterised by the massive area of the limestone landform and the lowland less than 1200 m elevation (Fang et al. 1994;Averyanov et al. 2003). The floristic region mainly covers the northernmost region from the North-west to North-east in Vietnam (Takhtajan 1986;Averyanov et al. 2003) that borders with the South-western Guangxi and South-eastern Yunnan in China (Wu and Wu 1998). In the last ten years, a large number of new species in different families have been discovered in the region, such as Begoniaceae, Gesneriaceae, Magnoliaceae etc. (Averyanov and Nguyen 2012;Chen et al. 2017;etc.).
Since 2016, for nearly three months, transboundary surveys have been conducted in Northwestern and Northeastern Vietnam (Bac Kan, Cao Bang, Lao Cai, Phu Tho, Tuyen Quang) and Southern China (Southwestern Guangxi and Southeastern Yunnan). After review of the type specimens and taxonomic publications within the regions (Gagnepain 1921;Irmscher 1939;Ho 1991;Nguyen 2004;Shui and Chen 2005;Truong et al. 2005;Nguyen and Tebbit 2006;Kiew 2007;Nguyen et al. 2010;Peng et al. 2014Peng et al. , 2015aHughes et al. 2015), seven new species of Begonia have been confirmed, and their sectional positions designated here (Doorenbos et al. 1998;Shui et al. 2002). Due to the taxonomic complexity of the genus (Thomas et al. 2011;Chung et al. 2014), the DNA samples of the above new species have also been collected and some possible different opinions will be issued about their systematic position in the broad context in the future.

Remarks.
The new species is similar to B. hahiepiana H.Q. Nguyen & Tebbitt in broadly ovate asymmetric leaves with slightly truncate or round apex and the corned berry fruit, but different from it in the broadly ovate or rotund leaves (vs. ovate), almost flat adaxial surface of leaves (vs. puckered), glabrous outer surface of petals (vs. with red trichomes), 4-loculed and glabrous berry fruit covered by dense white spots (vs. 3-loculed and pubescent fruit covered by the lax white spots).
Phenology. Flowering in April-May, fruiting in April-June.
Etymology. The epithet refers to the white spots on the fruit surface.
Habitat. The species only grows in deep ground amongst rocks in limestone forests. Distribution. The species occurs exclusively in Phu Tho Province, Xuan Son country, Xuan Son National Park of Vietnam.
Note. Currently six species from section Sphenanthera are recognised as occurring in Vietnam Nguyen & Tebbitt. Although this new species grows together with B. hahiepiana, it is easily distinguished by the glabrous and 4-loculed berry fruit, which has been discussed in the above diagnostic description. Within the Vietnamese species of the section, the stemless habit, the narrow inflorescence and the small horned appendage of the berry fruit indicate that the new species is also similar to Begonia ceratocarpa and B. balansana. The detailed comparison reveals that it is more similar to B. ceratocarpa with 3-4-loculed fruits than B. balansana with 6-7-loculed fruit. It is different from B. ceratocarpa in the broadly ovate or rotund leaves (vs. ovate), the unlobed leaf blade (vs. slightly lobed), round leaf top (vs. acuminate leaf top), petioles with red pubes (vs. with brown 1anes), 5 female tepals (vs. 3), densely white-spotted surface of berry fruit (vs. sparely spotted), truncate fruit top without a beak (vs. an acute fruit top with a beak). Begonia sect. Diploclinium A. DC.

Remarks.
The new species is similar to Begonia sinovietnamica C. Y. Wu in their habit and distribution ( Fig. 1; Fig. 2), but different from the latter species in expanding villous hairs on petiole and peduncles (vs. pubescent), 2 petals of the male flowers (vs. 4 petals), 2 petals of the female flowers (vs. 5 rarely 4 petals).
Phenology. Flowering in October-December, fruiting in November-January next year. Etymology. The epithet refers to the upward fruit when nearly mature ( Fig. 4-J). The erect case of fruit when nearly mature is unusual in the genus Begonia. The exceptional species is in some species in Begonia sect. Trachelocarpus (C. Müller) A. DC., such as Begonia lanceolata Vellozo in Brazil (Doorenbos et al. 1998;Tebbitt 2005).
Habitat. The species just grows on soil within the secondary tropical evergreen lowland rainforest and broad-leaved forests on the slopes and ridge of crystalline limestone with highly eroded earth at an elevation 400-700 m above sea level. Note. The new species should be a member of Begonia sect. Leprosae Y.M. Shui according to its clavate berry fruit (Shui et al. 2002). In the section, it is more similar to B. longicarpa and B. leprosa Hance than the other species. It is similar to B. longicarpa in the habitat of ground soil and different mainly in the petal number (5 vs. 3), the hairs of petiole (hispid vs. pubescent) and the morphology of the segments of placentation per locule (irregular placenta segments vs. 2 regular placenta segments per locule). It is also similar to B. leprosa in the morphology of the fruit and hairs on the petiole, but differs mainly in the habitat (ground soil vs. limestone surface), the abaxial surface of leaves (obviously reticulate nerves vs. obscurely reticulate nerves) and the petal number of the female ( Begonia sect. Coelocentrum Irmsch.
Phenology. Flowering in February-May, fruiting in May-June. Etymology. The epithet refers to the locality of the type specimens.
Habitat. The species only grows on the moist surface of shady cliffs at the entrance to shallow caves in a deep valley.
Distribution. The species occurs exclusively in Jingxi county of Guangxi in China. Note. In Begonia sect. Coelocentrum, the new species is similar to the population of B. daxinensis with a white area on the leaves, but differs mainly in its long glandular hairs (Wu and Ku 1997;Ku et al. 2004). In the latter species, the petals are covered abaxially by brown pubescence and are much larger than those of the new species. As to the lanceolate and colourful leaves, the new species is similar to Begonia locii C.-I Peng, C. W. Lin & H. Q. Nguyen, but different in the absence of glandular hairs of flowers (Peng et al. 2015a). Furthermore, as to the glandular pubes, the new species is also similar to B. filiformis Irmsch., but differs in the subglabrous adaxial surface and laxly pubescent abaxial surface of leaves (vs. densely pubescent adaxial and abaxial surface of leaves in the latter).
Phenology. Flowering in April-May, fruiting in May-June. Etymology. The epithet refers to the small size of leaves.
Habitat. The species just grows in limestone crevices of cliffs. Distribution. The species occurs exclusively in Nari county of Bac Kan Province in Vietnam.
Note. In Begonia sect. Coelocentrum, the new species is one of the smallest species in morphology. Its closest species with limited morphology is Begonia regosula Aver. also from Bac Kan Province (Averyanov and Nguyen 2012). In the new species, however, the wider interior petals and the obvious bifid stigma can separate it from B. regosula (Fig. 6). Begonia sect. Coelocentrum Irmsch.

Remarks.
The new species is similar to Begonia guangxiensis T.C. Ku in the dense white villous hairs on the whole plants, differs from the latter in the shorter hairs of plants (2.1-2.4 mm vs. 3.4-4.0 mm), its one obtuse leaf lobe (vs. 3-4 acute leaf lobes in B. guangxiensis), subequal three wings of the fruit (vs. unequal three wings), narrowly semi-lunar major wings (vs. broadly square major wings).
Phenology. Flowering in March-May, fruiting in April-June. Etymology. The epithet refers to the dense villous trichomes of the new species.
Habitat. The species only grows on cliffs in limestone forests. Distribution. The species occurs exclusively in Ba Be National Park (Cho Ra county) of Bac Kan Province in Vietnam.
Note. In Begonia sect. Coelocentrum, the new species is similar as Begonia guangxiensis in the dense hairy habit, mainly differing in the dense tubercular-based pubes on the abaxial surface of leaves (vs. villous trichomes in the latter species) and subequal wings (vs. unequal) (Wu and Ku 1997;Shui and Chen 2017). It is also similar as B. calciphila C.-I Peng in the shape and trichomes of leaves, but differs in 0.5-1.2 cm long stout internodes (vs. 1.5-4.5 cm long slender inter-nodes) and hairy flowers and fruits (vs. glabrous in the latter species) (Peng et al. 2015b). In Bac Kan Province, Vietnam, there are four new species already described, viz. B. regosula Aver., B. babeana Aver. & H.Q. Nguyen (Averyanov and Nguyen 2012) and two more new species described in this paper.

Remarks.
The new species is similar to Begonia crystinilla Y.M. Shui & W. H. Chen in the thick texture and shape of leaves, but differs in the flat adaxial surface of leaves with sparse setae (vs. the uneven with dense setae), pubescent abaxial surface of leaves (vs. lane), triangulate major wing of fruit (vs. semi-lunar).
Phenology. Flowering in August-November, fruiting in December-March next year. Etymology. The epithet refers to the reticulate pattern of nerves on the abaxial surface of leaves.
Habitat. The species only grows on rocks at the entrance to caves or on the shady slope in limestone forests.
Distribution. The species distributes to the border region between China and Vietnam, e.g. Jingxi county of Guangxi in China and Cao Bang and Tuyen Quang Province in Vietnam.