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

Abstract

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.

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, 2013; Begonia: Fang et al., 2006, Ku et al., 2006, 2008, Liu et al., 2005, 2007, Peng et al., 2005a, b, 2006, 2007, 2008a, b, 2010, 2012; Primulina: Xu et al., 2012, 2013; Oreocharis: 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.

Methods

Chromosome preparations

Somatic chromosomes of the new species, Begonia longgangensis (Peng et al., 22930) and B. ferox (Peng et al., 22956), were examined using root tips. The methods of pretreatment, fixation and staining for chromosome observations followed Hughes et al. (2011). Classification of the chromosome complements based on centromere position at mitotic metaphase follows Levan et al. (1964). Voucher specimens have been deposited in Herbarium, Biodiversity Research Center, Academia Sinica, Taipei (HAST).

Results and discussion

Species description

1. Begonia longgangensis C.-I Peng & Yan Liu, sp. nov. (sect. Coelocentrum) —TYPE: CHINA, Guangxi Zhuangzu Autonomous Region, Longgang Nature Reserve, elev. ca. 170 m, on limestone hill and cliff, 18 April 2011, Ching-I Peng, Kuo-Fang Chung, Yu-Song Huang, Bo Pan & Sheng-Yuan Liu 22930 (holotype: HAST; isotype: IBK). Figures 1 and 2.

Figure 1

Begonia longgangensis C.-I Peng & Yan Liu. A, Habit; B1, B1’, Leaf adaxial surface, showing margin and indumentum, B2, B2’, Leaf abaxial surface; C, Stipule; D, Staminate flower; E, Androecium; F, Stamens; G, Carpellate flower, side view, G’, face view; H, Style and stigmas; I, I’, Fruit; I, I1-6, Serial cross sections of a developing fruit; J, Seed. All from C.-I Peng et al. 22930 (HAST).

Figure 2

Begonia longgangensis C.-I Peng & Yan Liu. A, Habit and habitat; B, Cultivated plant at anthesis; C, Inflorescence; D, Stolon; E, Leaf adaxial surface; F, Stipule; G, Staminate flower, face view; H, Staminate flower, side view; I, Carpellate flower, face view; J, Carpellate flower, side view; K, Middle cross section of ovary; L, Capsule with persistent tepals; M, Seed SEM microphotograph (abortive seeds from a field-collected capsule). All from C.-I Peng et al. 22930 (HAST).

Monoecious herb, rhizomatous initially and becoming stoloniferous. Rhizomes 1–2 cm thick, internodes 1–1.5 cm long, sending out stolons to 150 cm or longer, 0.5-0.7 cm thick, villous, internodes 8-13(-17) cm long. Stipules eventually deciduous, ovate-triangular, 1–1.8 cm long, 1–1.2 cm wide, margin entire, strongly keeled, abaxially hairy along midrib, apex aristate, arista 0.4-0.7 cm long. Leaves alternate, petioles terete, (6-)9-18(-25) cm long, 0.7 cm thick, green or reddish, white villous when young, becoming brown tomentose, glabrescent; leaf blade asymmetric, broadly ovate to suborbicular, (10-)14.5-20 cm long, (7-)10.5-15 wide, apex acuminate, base strongly obliquely cordate, margin initially serrulate and shortly ciliate, becoming repand when mature, subcoriaceous, adaxially green, sparsely reddish-scabridulous and with minute processes, abaxially pale, tomentose on veins. Inflorescences axillary, arising directly from rhizome or stolons, dichasial cymes branched 3–4 times, peduncle 9–14 cm long, glabrous; bracts caducous. Staminate flower: pedicel 1.2-1.5 cm long, tepals 4, outer 2 broadly ovate, pinkish, 1–1.4 cm long, 1.2-1.4 cm wide, inner 2 elliptic, white, 0.8-1.2 cm long, 0.4-0.5 cm wide; androecium actinomorphic, spherical, ca. 0.5 cm across; stamens 40–60; filaments fused into a column ca. 0.2 cm long; anthers 2-locular, obovate, connective obtuse at apex. Carpellate flower: pedicel 1.4-1.9 cm long, tepals 3, outer 2 broadly ovate to suborbicular, pinkish, 0.7-1.2 cm long, 0.8-1.2 cm wide, inner 1 elliptic, white, 0.6-1 cm long, 0.3-0.5 cm wide; ovary trigonous-ellipsoid, 0.7-1.1 cm long, 0.3-0.5 cm across (wings excluded), reddish, glabrous, 3-winged; wings unequal, greenish, lateral wings narrower, 0.2-0.3 cm tall, abaxial wing crescent-shaped, 0.3-0.5 cm tall; styles 3, fused ca. 0.5 cm long at base, stigma spirally twisted. Capsules nodding, 0.9-1.3 cm long, 0.5 cm across (wings excluded), apex with persistent tepals; wings unequal, lateral wings 0.3 cm tall, abaxial wing crescent-shaped, 0.3-0.6 cm tall; seed plump or abortive. Somatic chromosome number, 2n = 30, 45 (Figure 3).

Figure 3

Somatic chromosomes at metaphase of Begonia longgangensis (from Peng et al. 22930, HAST). A and B, micrographs: A, 2n = 30; B, 2n = 45. Arrows indicate longer metacentric chromosomes.

Chromosome cytology

Our study of the somatic chromosomes at metaphase of Begonia longgangensis revealed different ploidy levels in plants of the same population (2n = 30, 45) (Figure 3). Previously, a few cases were documented in the genus Begonia in which infraspecific polyploidy occurs, e.g. B. monophylla with 2n = 28, 56 (Legro and Doorenbos, 1969); B. rex with 2n = 24, 48 (Sharma, 1970); B. squamulosa with 2n = 38, 76 (Arends, 1992). This is the first confirmed report of a naturally occurring triploid in Begonia sect. Coelocentrum.

The diploid (2n = 30) has two longer metacentric chromosomes ca. 1.4-1.5 μm long (Figure 3A: arrows) and 28 shorter chromosomes ca. 1.0-1.2 μm long. By contrast, the triploid (2n = 45) has three longer metacentric chromosomes, ca. 1.7 μm long (Figure 3B: arrows), and 42 shorter chromosomes, ca. 0.9-1.3 μm long. The centromere positions of most chromosomes in both diploid and triploid plants could not be determined. Satellites were not observed.

All 19 species of Begonia sect. Coelocentrum that we studied cytologically uniformly had the chromosome number of 2n = 30 (Peng et al., 2012), of which seven were known to have bimodal karyotypes with two longer metacentric chromosomes in the chromosome complement. Since there are diploid and triploid plants within a natural population of B. longgangensis, by comparison of the number of longer metacentric chromosomes, the 2n = 45 plant likely represents intraspecific autotriploid.

Additional specimens examined

CHINA. Guangxi Zhuangzu Autonomous Region, Longzhou County, Zhubu Xiang, Longgang Cun, Lenglei Tun, 6 Oct 1979, Longgang Exped. 20386A (GXMI); Longzhou County, Longgang Nature Reserve, elev. ca. 170 m, on limestone hill and cliff, 18 April 2011, flowering specimen pressed from cultivated plant in 28 May 2013, Ching-I Peng, Kuo-Fang Chung, Yu-Song Huang, Bo Pan & Sheng-Yuan Liu 22930-A (HAST).

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).

Figure 4

Distribution of Begonia nonggangensis (●), B. liuyanii (☆), B. ferox (▲) in Guangxi Zhuangzu Autonomous Region, China and B. nahangensis (★) in Vietnam.

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.

Notes

Begonia longgangensis somewhat resembles B. liuyanii in the broadly ovate to suborbicular leaf shape (Peng et al., 2005), differing in the rhizomes that send out elongate stolons; much smaller leaves, sparsely reddish-scabridulous leaf adaxial surface with minute processes, tomentose only on veins of leaf abaxial surface; dichasial inflorescence, pink flowers and glabrous peduncle, tepal and ovaries. A detailed comparison is provided in Table 1.

Table 1 Comparison of Begonia longgangensis with B. liuyanii

2. Begonia ferox C.-I Peng & Yan Liu, sp.nov. (sect. Coelocentrum) —TYPE: CHINA. Guangxi Zhuangzu Autonomous Region, Longzhou County, Chunxiu Headwater Forest Nature Reserve, elev. ca. 130 m, on forest floor, limestone rock surface, 20 April, 2011. Ching-I Peng, Kuo-Fang Chung, Yu-Song Huang & Bo Pan 22956 (holotype: HAST; isotypes: E, IBK, PE). Figures 5 and 6.

Figure 5

Begonia ferox C.-I Peng & Yan Liu. A, Habit; B, Leaf; C, Leaf cross section; D, Stipule; E, Bracts; F, Staminate flower; G, Androecium; H, Stamen; I, I’, Carpellate flower; J, J’, Style and stigmas; K, K’, K”, Serial cross sections of an immature capsule. All from C.-I Peng et al. 22956 (HAST).

Figure 6

Begonia ferox C.-I Peng & Yan Liu . A, Habit and habitat; B, Cultivated plant at anthesis; C, Leaf abaxial surface and young leaves with dense hairs; D, Rhizome and stipules; E, Staminate flower, face view; F, Staminate flower, side view; G, Carpellate flower, face view; H, Carpellate flower, side view; I, Leaf adaxial surface with bullae; J, Leaf cross-section, showing abaxial surfaces of bullae; K, Inflorescence; L, Bract; M, Fruit; N, Cross section of ovary; O, Seed SEM photomicrograph. All from C.-I Peng et al. 22956 (HAST).

Monoecious rhizomatous herb. Rhizome stout, creeping, 1-2(-2.5) cm thick, to 40 cm long, internodes 1–1.5 cm long, villous near base of petiole. Stipules eventually deciduous, ovate-triangular, 1–1.7 cm long, 1.1-1.5 cm wide, herbaceous, strongly keeled, abaxially hairy along midrib, apex aristate, arista ca. 0.2 cm long. Leaves alternate, petiole terete, 10-23(-27) cm long, 0.4-0.7 cm thick, villous when young, turning brownish tomentose; leaf blade asymmetric, ovate, (11-)14-19 cm long, 8–13 cm wide, apex acuminate, base strongly oblique-cordate, margin repand, chartaceous, villous when young, adaxially green, surface bullate, intercostal area densely dotted with blackish-brown and hair-tipped bullae, individual bullae conical, tip reddish, (0.3-)0.8-1.3 cm high, (0.3-)0.8-1.2(-1.5) cm across, abaxially pale green, reddish on veins and bullae region, tomentose on veins. Leaves of juvenile plant with few or no bullae. Inflorescences axillary, dichasial cymes, arising directly from rhizome, branched 3–4 times; peduncle 5–13 cm long, tomentose; bracts and bracteoles caducous, yellowish, bracts narrowly ovate, 1–1.2 cm long, 0.4-0.6 cm wide, boat-shaped, veins reddish, margin fimbriate, bracteoles oblong, ca. 0.3 cm long, 0.1 cm wide. Staminate flower: pedicel ca. 1.5 cm long, tepals 4, outer 2 broadly ovate, 0.9-1.1 cm long, 0.6-1 cm wide, abaxially yellowish-reddish, sparsely setulose, inner 2 elliptic, white, 0.7-1.1 cm long, 0.4 cm wide; androecium actinomorphic, spherical, ca. 0.4 cm across; stamens 65–85; filaments fused at base into a column ca. 0.2 cm long; anthers obovate, 2-locular. Carpellate flower: pedicel 1.5-1.6 cm long, tepals 3, outer 2 suborbicular or broadly ovate, pinkish-white, 0.8-1.1 cm long, 0.7-1.1 cm wide, inner 1 elliptic, white, 0.8-0.9 cm long, 0.3-0.4 cm wide; ovary trigonous-ellipsoid, 1.3-1.4 cm long, 0.4 cm thick (wings excluded), reddish, 3-winged; wings unequal, greenish-yellow, lateral wings narrower, 0.4-0.5 cm tall, abaxial wing crescent-shaped, ca. 0.6 cm tall, 1.5-1.6 cm wide; styles 3, fused at base, yellow or greenish, ca. 0.4 cm long, stigma spirally twisted. Capsule trigonous-ellipsoid, 1–1.5 cm long, 0.2-0.5 cm thick (wings excluded), greenish or reddish when fresh; wings unequal, lateral wings 0.3-0.5 cm tall, abaxial wing crescent-shaped, 0.6-0.9 cm tall. Seeds numerous, brown, ellipsoid, ca. 0.5 mm long, 0.3 mm thick. Somatic chromosome number, 2n=30 (Figure 7).

Figure 7

Somatic chromosomes at metaphase of Begonia ferox C.-I Peng & Yan Liu (2 n = 30, from C.-I Peng et al. 22956 , HAST). Arrows indicate a pair of long, metacentric chromosomes.

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). Among them, eight taxa, namely B. arachnoidea, B. debaoensis, B. kui, B. ningmingensis var. bella, B. pengii, B. picturata, B. umbraculifolia, and B. longgangensis (here reported) have a bimodal variation in chromosome length with two longer metacentric chromosomes. The karyomorphological feature of B. ferox reported here agreed with the previous observations.

Additional specimens examined

CHINA. Guangxi Zhuangzu Autonomous Region, Longzhou Xian, Chunxiu Headwater Forest Nature Reserve, elev. ca. 130 m, on forest floor, limestone rock surface, 20 April 2011. Flowering specimens pressed from cultivated plants in February, 2013, Ching-I Peng, Kuo-Fang Chung, Yu-Song Huang & Bo Pan 22956-A (HAST, IBK).

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.

Phenology

Flowering January-May; fruiting April-July.

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 Table 2.

Table 2 Comparison of Begonia ferox with B. nahangensis