Begonia hypoleuca Y.H.Tan & H.B.Ding, 2020

Ding, Hong-Bo, Maw, Mya Bhone, Yang, Bin, Bouamanivong, Somsanith & Tan, Yun-Hong, 2020, An updated checklist of Begonia (Begoniaceae) in Laos, with two new species and five new records, PhytoKeys 138, pp. 187-201 : 187

Begonia hypoleuca Y.H.Tan & H.B.Ding sp. nov. Figure 2

sect. Reichenheimia (Klotzsch) A. de Candolle

Diagnosis.

The new species is mostly similar to B. henryi Hemsley (1887: 322), but differs by its glabrous leaves, petiole with linear red dots and pubescent, slightly denticulate leaf margin and fewer stamens.

Type.

Laos. Luang Namtha Province, Nam Ha National Biodiversity Conservation Area, Nam O. Village, 20°04'48.16"N, 101°06'58.46"E. 656 m elev., 24 October 2018, Y.H. Tan, B. Yang, H.B. Ding & X.D. Zeng L0792 (holotype: HITBC!).

Description.

Monoecious herb, stemless, tuber small, globose with fibrous roots, 10-13 mm in diameter. Stipule: caducous. Leaf: petiole 7-10 cm long, succulent, with reddish linear dots, sparsely pubescent or subglabrous. Blade slightly triangular ovate or broadly ovate, 6-12 × 5-8.5 cm, base cordate, apex acuminate, margin slightly denticulate, upper surface green, lower surface paler or silver, glabrous, venation palmate-pinnate, midrib pale green, lateral veins 4-6 pairs. Inflorescence axillary, cymose, peduncle ca. 6 cm long, reddish, glabrous, branching 2-4 times, 2-6 male flowers, ca. 2 pistillate flowers, bracts caducous, ca. 2 × 1 mm. Staminate flower: pedicel 1.0-1.2 cm long, membranous, reddish at the basal part and pink, glabrous, tepals 2, pink, margin entire, glabrous on both surfaces, broadly ovate, 12 × 10 mm, apex acute, base rounded; stamens 10-15, filaments 1.5-2 mm long, anthers 1-1.5 mm, ellipsoid, yellow. Pistillate flower: pedicle ca. 1.8 cm long, reddish to pink, tepals unknown, ovary 3-locular, placentae axial, entire, styles 3. Capsule pale green, nodding, ellipsoid, dorsal wing enlarged, 7-10 mm long, two lateral wings, smaller, 2-3 mm long.

Phenology.

Flowering and fruiting in October-November.

Distribution.

The species is known only from the type locality, Luang Namtha Province, Nam Ha National Biodiversity Conservation Area, Laos.

Ecology.

The species was collected on shaded moist limestone rock surfaces of stone forest at 656 m elevation.

Etymology.

The specific epithet ' hypoleuca ' refers to the lower surface of its paler or silver leaf.

Conservation status.

Data Deficient (DD). Begonia hypoleuca has been collected on only one occasion from the type locality. However, the type locality is located in the Nam Ha National Biodiversity Conservation Area and we did not discover any strong pressure on the species. Thus, the species preliminarily has been assigned in the Data Deficient (DD) category as being appropriate according to the guidelines for using the IUCN Red List Categories and Criteria ( IUCN 2017).

Notes.

Begonia hypoleuca is most similar in morphological characteristics to B. henryi Hemsl. under the section Reichenheimia . It can, however, be distinguished by the following characteristics, including reddish linear red dots on petiole (vs. without), sparsely pubescent on petiole (vs. brown villous), slightly denticulate leaf margin (vs. crenate), glabrous leaves (vs. pubescent), leaf upper surface green (vs. green with dark green patches), lower surface pale green (vs. pale green with reddish patches), male flower tepals broadly ovate (vs. oblate-orbicular), apex acute (vs. rounded), stamens number fewer 10-15 (vs. up to 30).

Figures

Figure 2. Begonia hypoleuca Y. H. Tan & H. B. Ding, sp. nov. A habitat B flowers (front view) C flowers (lateral view) D habit E inflorescence F leaves G tepals of staminate flower (back view) H stamens with peduncle I tepals of staminate flower (front view) J mature fruit with peduncle K mature fruit L-N serial cross sections of ovary. Photographed by H. B. Ding.