Begonia tamdaoensis, Peng, Ching-I, Yang, Hsun-An, Kono, Yoshiko, Jung, Ming-Jer & Nguyen, Tien Hiep, 2015

Peng, Ching-I, Yang, Hsun-An, Kono, Yoshiko, Jung, Ming-Jer & Nguyen, Tien Hiep, 2015, Four new species of Begonia (Begoniaceae) from Vietnam: B. abbreviata, B. calciphila, B. sphenantheroides and B. tamdaoensis, Phytotaxa 222 (2), pp. 83-99 : 94-97

4. Begonia tamdaoensis C.-I Peng, sp. nov. (sect. Platycentrum ) ( Figs 10 , 11 )

Type: — VIETNAM. Vinh Phuc Province, Tam Dao District . On rock surface along roadside slope, in broadleaf forest, elev. 1050 m, common locally. Living collection made on 21 Mar 1997 ; type specimens (in flower) pressed from plants cultivated in experimental greenhouse, 25 Oct 2002, Ching-I Peng 16634 (holotype: HAST 139795 ; isotype: A, E, HN, K, KEP, MO, P). Ξθkȁầ

Herbs monoecious, perennial, rhizomatous. Rhizomes 4–7 mm across, to 10 cm long; erect stems seen only at anthesis, to 27 cm tall, ca. 4 mm thick, hispid. Stipules narrowly ovate to triangular, ca. 5 mm long, 4 mm wide, margin entire, keeled, apex aristate, arista ca. 1 mm long, sparsely hispid. Leaves alternate, petiole to 15 cm long, hispid; leaf blade ovate or elliptic, asymmetric, 8–12 cm long, 5–8 cm wide, glabrous or subglabrous above, tomentose along nerves beneath, base slightly obliquely-cordate, margin very shallowly divided, irregularly serrulate and ciliate; apex acute to acuminate; venation palmate-pinnate. Inflorescences axillary, protandrous, to 25 cm long, with 4–12 flowers; peduncles 5–21 cm long, hispid; bracts persistent, lanceolate to triangular, apex acuminate, to 5 mm long, margin sparsely fimbriate. Staminate flower: pedicel 1.2–2.3 (–2.8) cm long, glandular-hispid; tepals 4, pink, apex obtuse, outer 2 ovate or narrowly so, 0.8–2 cm long, 0.4–1.2 cm wide, hispid abaxially, inner 2 narrowly oblong or oblanceolate, 0.8–1.8 cm long, 2–6 mm wide; androecium zygomorphic, stamens 12–35, yellow, clavate; filaments 0.5–2.3 mm long, fused at base, anthers 1.6–1.8 mm long. Carpellate flower: pedicel 1.5–2.1 cm long, glandularpilose; ovary unequally 3-winged, glandular-hispid, 2-locular; placentae axile, bilamellate; tepals 5, pink, unequal, oblanceolate, oblong or ovate, 1.5–1.8 cm long, 0.4–1.3 cm wide, hispid outside, apex obtuse; styles 3, fused at base, 2-cleft, stigmas in a spiralled band around style apex. Capsule nodding, unequally 3-winged, abaxial wing ligulate or falcate, 11–19 mm tall, lateral wing ca. 3 mm tall.

Ecology & Distribution:— Known only from Tam Dao, Vinh Phuc Province, Vietnam ( Fig. 3 ). On rock face on roadside slope, in broadleaf forest, elev. 1050 m, locally common.

Etymology:— The specific epithet refers to the type locality, Tam Dao.

Additional specimen examined:— VIETNAM. Vinh Phuc Province, Tam Dao District. On rock face along roadside slope, in broadleaf forest, elev. 1050 m, common locally, 21 Mar 1997, Ching-I Peng 16634 ( HAST) ; Vinh Phuc Province, Tam Dao District . Near base of rocky slope, elev. ca. 1000 m. Living collection made on 22 Mar 1997, specimens pressed from plant cultivated in experimental greenhouse, 29 Oct 2007, Ching-I Peng 16638 ( HAST) ; Approximately 100 km NNW of Hanoi, Tam Dao Forest Reserve , on trail approximately 0.5 km S of bridge over Suoi B’ac River. Along trail on rocky soil, 21°27’09”N, 105°39’09”E, elev. 990 m. 9 Sep 1993. D. K. Harder et al. 1805 ( HAST) ; Vinh Phuc Province, Tam Dao National Park , 6 Nov 2009, Pi-Fong Lu s. n., specimens pressed from plant cultivated in experimental greenhouse, 15 May 2015, Ching-I Peng 22285 ( HAST) .

Leaf anatomy and vestiture:— Adaxial surface with glandular trichomes ( Fig. 4J ); cross section ca. 450 μm thick, upper epidermis biseriate, with a layer of thick hypodermis under upper epidermis, lower epidermis single-layered ( Fig. 4K ); abaxial surface with glandular trichomes, stomata complex single, helicocytic, flat, subsidiary cell (5–)6 ( Fig. 4L ).

Chromosome cytology:— Chromosomes of most species of Begonia are small (<2 μm), difficult to stain, and karyotypes are mostly impossible to determine ( Peng et al. 2014b). The somatic chromosome number of B. tamdaoensis was determined as 2 n = 18 ( Fig. 5D ). The chromosomes are large and clearly analyzable. Among the 18 chromosomes, six were metacentric (m) and about 3.0–4.5 μm in length (Nos. 1–6 in Fig. 5 D’), eight were submetacentric (sm) and 2.0–3.4 μm in length (Nos. 7–14 in Fig. 5 D’), two were subtelocentric (st) and about 3 μm in length (Nos. 15 and 16 in Fig. 5 D’) and the remaining two were telocentric chromosomes (t) and about 1.8 μm in length (Nos. 17 and 18 in Fig. 5 D’). Secondary constrictions (SC) were observed at the interstitial regions of the long arms of the largest two median chromosomes (Large arrows in Fig. 5D ) and at the distal regions of long arms of two median chromosomes (Middle arrows in Fig. 5D ). The karyotypic formula of B. tamdaoensis is 2 n = 18 = 6m (4SC)+8sm+2st+ 2t.

As noted above, the predominant chromosome number in sect. Platycentrum (including B. sphenantheroides , the new species documented in this paper) is 2 n = 22. Our observation of 2 n = 18 in B. tamdaoensis is exceptional, which however corresponds to that of B. purpureofolia S.H. Huang & Y.M. Shui reported by Nakata et al. (2007). Begonia wui-senioris C.-I Peng (2014: 55-13: 2), another member of sect. Platycentrum , has the lowest chromosome number, 2 n = 14, for the genus ( Peng et al. 2014b).

Notes:— Begonia tamdaoensis is assignable to sect. Platycentrum by being rhizomatous, protandrous, staminate flowers basal and pistillate flowers distal, ovaries 2-locular and placentas with two branches, capsules pendulous, 2-loculate and wings very unequal ( Doorenbos et al. 1998). The capsules are recurved, which is likely an adaptation for rain splash dispersal (Tebbit et al. 2006). However, it is unusual in having 3-styled carpellate flowers. Begonia versicolor Irmscher (1939: 546) is the only other species in sect. Platycentrum that is known to have 3-styled carpellate flowers and 2-loculed ovaries ( Shui et al. 2002; Gu et al. 2007).

Begonia tamdaoensis resembles B. oreodoxa Chun & F. Chun ex C.Y. Wu & T.C. Ku (1995: 274) in SE Yunnan ( China) and northern Vietnam in aspect and being very pubescent, but is distinguished by the very shallowly cordate leaves (vs. cordate), bracts fimbriate (vs. incised), carpellate flower with 5 tepals (vs. 4 or rarely 3) and 3 styles (vs. 2), placentas axile throughout (vs. axile for the most part, but parietal near summit of ovary).

Figures

FIGURE 3. Distribution map of Begonia abbreviata (■), B. calciphila (Ì), B. sphenantheroides (●) and B. tamdaoensis (▲) in Vietnam.

FIGURE 4. SEM microphotographs of Begonia leaves. A–C, B. abbreviata; D–F, B. calciphila; G–I, B. sphenantheroides; J–L, B. tamdaoensis; A, D, G, J, Leaf adaxial surfaces; B, E, H, K, Leaf cross-sections; C, F, I, L, Leaf abaxial surfaces. Scale bars = 200 μm.

FIGURE 5. Somatic chromosomes at metaphase of Begonia. A. B. abbreviata (2n = 30: NTH 5917); B. B. calciphila (2n = 30: Peng et al. 20226); C. B. sphenantheroides 2n = 22: Peng et al. 20216); D. B. tamdaoensis (2n = 18: Peng et al. 16638); B’, C’, D’, somatic chromosomes serially arranged by chromosome length and centromere position. Scale bars: B’, C’= 2 μm; D’ = 5 μm. Large arrows indicate a pair of the largest metacentric chromosomes with secondary constrictions (SC) at interstitial regions of the long arms; medium arrows indicate metacentric chromosomes with SC at distal regions of the long arms. Small arrows, large arrowheads and small arrowheads indicate metacentric chromosomes, subtelocentric chromosomes and telocentric chromosomes, respectively.

FIGURE 10. Begonia tamdaoensis C.-I Peng. A, Habit; B, Staminate flower, face view; B’, Staminate flower, back view; C, Carpellate flower; D, Androecium; E, Styles and stigma; F, Bract; G, G’, stipules; H, Cross section of ovary; I, I’, Stamens; J, Showing indumentum on petiole; K, Leaf adaxial surface; K’, Leaf abaxial surface; L, Fruit. All from C.-I Peng16634 (HAST). Line drawing by Ya-Wen Hsueh.

FIGURE 11. Begonia tamdaoensis C.-I Peng. A, Habit; B, Inflorescence, showing indumentum on pedicels and tepals; C, Rhizome, showing indumentum on petioles; D, Staminate flower, face view; E, Carpellate flower, face view; F, Bracts and pedicels, showing glandular trichomes; G, Leaf abaxial surface; H, Staminate flower, side view; I, Carpellate flower, side view; J, Fruit; K, Cross section of ovary. All from C.-I Peng 16634 (HAST).