Begonia parvibracteata X.X.Feng, R.K.Li & Z.X.Liu, 2022

Feng, Xin-Xin, Huang, Xiao-Feng, Huang, Yu-Ni, Liu, Zhi-Xian, Li, Ren-Kun, Zhou, Jin-Ye, Guo, Wei, Chen, Xiao-Yan & Tian, Dai-Ke, 2022, Begonia parvibracteata, a new species in Begonia sect. Platycentrum (Begoniaceae) from Guangxi of China, based on morphological and molecular evidence, PhytoKeys 214, pp. 27-38 : 27

Begonia parvibracteata X.X.Feng, R.K.Li & Z.X.Liu sp. nov.

Figs 1 , 2 Chinese name: 小苞秋海棠

Type.

China Guangxi, Longzhou County (龙州县), Zhubu Town (逐卜乡), Bannong Village (板弄屯), Yinghuagu Tourist Resort , 22°33'51"N, 106°57'03"E, (Fig. 3 ), 263 m alt., in shaded environment of limestone forest, October , 2021, Xin-Xin Feng , Ren-Kun Li & Zhi-Xian Liu (holotype: 835307, IBSC!; isotype: SYS!). Longzhou County (龙州县), Zhubu Town (逐卜乡), Pona Village (坡那屯), Nonggang National Nature Reserve , 22°39'03"N, 106°57'18"E, 190 m alt., on rock under limestone forest, 18 May 2020, Dai-Ke Tian & Jinye Zhou TDK4119 (CSH!) .

Diagnosis.

Begonia parvibracteata morphologically resembles B. subhowii and B. psilophylla in rhizome and leaf characters. However, it has narrowly oblique-ovate asymmetric leaf blades, 4 (rarely 6) tepals in pistillate flowers and small (6-8 × 3-5 mm) bracts in inflorescences. These characters differ from the widely ovate leaf blades, 5 (rarely 6) tepals of pistillate flowers, and distinctly large bracts in inflorescences of B. subhowii . B. parvibracteata is dissimilar to B. psilophylla in its 4 (rarely 6) tepals in pistillate flowers and asymmetric, narrowly oblique-ovate leaf blade.

Begonia parvibracteata forms a monophyletic group clustered with B. cucurbitifolia in the phylogenic tree, but the latter has nearly symmetric, 3-4 lobed leaf blade, 5-tepaled pistillate flower, definitely differing from the new species.

Description.

Perennial evergreen herb, monoecious, 15-30 cm tall. Rhizome creeping, ca. 8.5-12 cm long and 6-10 mm thick, internode short or not obvious; erect stem only seen at anthesis, ca. 7.5-10 cm long, internodes 1-2 (3), green to reddish-green, glabrous. Stipules brownish-red, translucent, ovate-triangular, ca. 8-10 × 4-5 mm, glabrous. Leaves 3-6 basal and 2-3 aerial, petiole yellowish-green, 18-22 cm long, glabrous; blade asymmetric, ovate to narrowly ovate, 14-16 × 7.5-9 cm; apex acuminate to caudate, base oblique-cordate; leaf margin usually almost entire or occasionally crenate; venation palmate with 6-8 primary veins, adaxially slightly concave, abaxially convex; leaf blade fleshy, abaxially pale-green, glabrous; adaxially green, glabrous. Inflorescences arising from erect stem; dichasial cymes branching one to two times, peduncle 10-12 cm long, glabrous; flowers unisexual, 3-7 flowers per inflorescences; bracts membranous, triangular to widely ovate, brownish-red, 6-8 × 3-5 mm, glabrous. Staminate flower: pedicels pale green, ca. 2-2.3 cm long, glabrous; tepals 4, outer 2 tepals ovate to circular, 13-21 × 12-20 mm, adaxially concave, pinkish-white, abaxially convex, pinkish-white, red hispid; inner 2 obovate, 10-18 × 8-12 mm, margin irregularly entire, white, glabrous; androecium cylindrical, ca. 6.6-7.5 mm across; stamens numerous, ca. 2-2.5 mm long, anthers yellow, clavate, base cuneate, ca. 1.5 mm long. Pistillate flower: pedicels pale green, ca. 2-2.6 cm long, glabrous; tepals 4, occasionally 6, white, irregularly ovate, obovate or cuneate, sub-equal, 18-20 × 10-15 mm, glabrous; ovary yellowish-green, trigonous-ellipsoid, 11-12 × 5-6 mm (wings excluded), glabrous; 2-loculed, placentae axillary, placentae bifid per locule; styles 2, fused at base, yellow, ca. 5-6 mm long, apically Y-shaped, stigma U-shaped, spirally twisted. Capsules nodding, trigonous-ellipsoid, ca. 11-13 × 5-6.5 mm (wings excluded), yellowish-green, glabrous, unequally 3-winged, abaxial wing triangular to ligulate, ca. 10-13 mm long; lateral wings lunate, 3-6 mm long.

Distribution and habitat.

Currently known from four localities in Longzhou County and Daxin Countym Guangxi, China. It usually grows on rocks or rock cracks in limestone under forest.

Phenology.

Flowering September-October, fruiting October-December.

Etymology.

The specific epithet " parvibracteata " refers to the short small bracts of the new species. The Chinese name is given as “小苞秋海棠” ( Begonia with small inflorescence bracts).

Conservation status.

There are three populations with approximately 1000 individuals found in Longzhou County. Another one population with approximately 500 individuals is distributed in the Encheng National Nature Reserve, Daxin County. Some plants of this begonia are over-collected and sold in the local medicinal herb market of Longzhou County. According to the IUCN Red List Categories and Criteria ( IUCN 2022), B. parvibracteata should be assessed as "Vulnerable (VU B1, B2 ab (i, iv, v), D2)" due to its narrow distribution and the disturbance by human activities.

Molecular analysis

The aligned matrix of the ITS sequence data was 727 bp long. The result of Bayesian Inference analysis is shown in Fig. 4 . Begonia sect. Platycentrum appears monophyletic with a high Bayesian posterior probability (bpp = 1) (Fig. 4 ). The three samples of the putative new species form a monophyletic group clustered with B. cucurbitifolia (bpp = 0.89). Begonia subhowii with the highest morphological similarity to B. parvibracteata formed another subclade.

The nodes with bpp <0.50 have been collapsed. Sectional placement of taxa is indicated by the following abbreviations: Coe ( Coelocentrum ), Dip ( Diploclinium ), Pla ( Platycentrum ), Rei ( Reichenheimia ) and Pel ( Peltaugustia ). The numbers after the species names indicate different populations. The samples of the new species are marked with stars.

Figures

Figure 1. Begonia parvibracteata drawn by Yunxiao Liu A khabit B staminate inflorescence C, D front and back views of staminate flower E lateral view of staminate flower F stamen G, H front and back views of pistillate flower with 4 tepals I front view of pistillate flower with 6 tepals J cross section of ovary K styles and stigmas L stigmas M abaxial view of capsule showing wings N lateral view of capsule showing two shorter wings.

Figure 2. Habitat and morphology of Begonia parvibracteata A habitat B flowering plant C creeping rhizome D shoot top with stipule E leaf blade (adaxial) F, G leaf blade (abaxial) H erect stem with inflorescence I, J young inflorescence and bract; K, L front and back views of staminate flower with 4 tepals M lateral view of staminate flower N stamens O, P front and back views of pistillate flower with 4 tepals Q front view of pistillate flower with 6 tepals R cross section of ovary S stigmas T, U immature capsule V dried mature capsule (Photos by Z. X. Liu).

Figure 3. Distribution of B. parvibracteata, B. subhowii, B. psilophylla and B. cucurbitifolia.

Figure 4. Bayesian Inference of the phylogenetic position of the newly-described B. parvibracteata within sect. Begonia Platycentrum, based on nuclear ITS sequences.