Begonia menchunaensis P.Gyeltshen & M.Hughes, 2022

Gyeltshen, Phub, Hughes, Mark, Zangpo, Pema, Jamtsho, Sherab, Phuntsho, Tashi, Choden, Tshering, La, Cheten & Wangchuk, Tandin, 2022, ONE NEW SPECIES AND FOUR NEW RECORDS OF BEGONIA (BEGONIACEAE) FROM BHUTAN, Edinburgh Journal of Botany 79 (1922), pp. 1-18 : 2-8

Begonia menchunaensis P.Gyeltshen & M.Hughes , sp. nov. [§ Diploclichium]

Begonia menchunaensis is similar to B. picta Sm. but is distinguished from it by its moniliform tubers (vs single globose tubers); longer petioles up to 10–55 cm (vs 5–12(–20) cm), which are glabrous (vs sparsely puberulous); outer tepals in male and female flowers with an acUte apex (vs roUnded); and immatUre ovaries with simple red setose hairs (vs white fimbriate villose hairs). – Type: BhUtan, PUnakha District, Toedpisa Block, Menchuna , 2284 m, 24 ix 2021, P. Gyeltshen 067-068 (holotype THIM [ THIM17728 ], isotype THIM [ THIM18604 ]). Figures 1, 2, 3, 4 .

Monoecious, tuberous herb, up to 25 cm tall. Tuber stout, moniliform, each section 1–3 cm in diameter, with nUmeroUs fibroUs roots. Stem 1- or 2-branched, terete, glabrous, up to 20 cm long. Leaves: lamina symmetrical, broadly ovate to triangular-ovate, 15–35 × 10–26 cm, apex acuminate, base cordate, margin shallowly lobed, bidenticulate; adaxial surface green to olive green, white pilose, abaxial surface pale green to brownish green, venation palmate-pinnate, veins c.8, prominent beneath; petiole 10–55 cm long, up to

1.2 cm in diameter, fleshy, pale green to reddish brown, glabroUs. Inflorescence terminal, a compressed cyme, appearing Umbellate, bisexUal, protandroUs, 2- to 6-flowered; pedUncle pilose when young, unbranched, 5–16 cm long, terete, pale green to lightly brownish red. Staminate flower: pedicels 2.5–4 cm long, erect or curved downwards, pilose, pale green to light brownish green; tepals 4, outer tepals broadly ovate to triangular-ovate, 1.7–2.1 × 1.5–2 cm, apex broadly acute, margin entire or serrate, outer surface sparely red setose, inner surface glabrous, pale pink to white; inner tepals elliptic, 1.2–1.6 × 0.5–1 cm, apex acute, margin entire, outer surface glabrous or a few red setose, whitish pink to white; androecium symmetrical,> 60 stamens, bright yellow; filaments clUstered at the base on a column, free, unequal, 0.5–2 mm long; anthers obovate, 1–1.6 mm long, connective rounded, apex obtuse or truncate, dehiscing through lateral slits. Pistillate flower: pedicels 1.5–3 cm long, pilose, pale green or greenish red; ovary green, with 3 unequal wings, with simple red setose hairs, denser on the locular portion; 3-locular, placentation axillary, 2 branches per locule; tepals 5 (or 6), unequal, outer 3 tepals ovate to elliptic-ovate, 1.5–1.8 × 1–1.3 cm, apex acute, margin serrate, outer surface red setose, inner tepals 2 or 3, unequal, elliptic, 1–1.5 × 0.5–0.8 cm, apex acute, margin entire, glabrous, same colour as staminate flower; styles 3, fused at the base, dark yellow, deeply forked once and twisted twice. Capsule oblong-ellipsoid, 1–1.5 × 0.5–0.7 cm, green, with red setose hairs, wings slightly extending along the pedicel, unequal; dorsal wing, narrowly triangular, 3.5–4.6 × 1–1.5 cm, lateral 2 wings short triangular, 8–12 × 2–9 mm, sparsely red setose, warty.

Altitudinal range. 2270–2300 m.

Phenology. Flowering in September, fruiting from September to October. Distribution. Begonia menchuaensis is endemic to Bhutan and currently known only from the type locality at Mechuna, Punakha District ( Figure 5) .

Habitat. Lithophytic on rocks near streams in cool broadleaved forest (see Figure 1). Associated species are Ageratina adenophora (Spreng.) R.M.King & H.Rob. , Anaphalis margaritacea (L.) Benth. & Hook.f., Astilbe rivularis Buch. -Ham. ex D.Don, Begonia josephi A.DC. , Girardinia diversifolia (Link) Friis , Gonostegia triandra (Blume) Miq. , Impatiens racemosa DC. , Koenigia mollis (D.Don) T.M.Schust. & Reveal and Persicaria chinensis (L.) H.Gross.

Etymology. The specific epithet is derived from the name of the type locality, MenchUna in Punakha District, Bhutan.

Proposed IUCN conservation category. Begonia menchunaensis is assessed as Critically Endangered (CR). We have explored the surrounding areas of the type locality and other places with similar habitat in search of this new species, but Begonia menchunaensis is currently known from only one population consisting of c.100 mature individuals. The area of occupancy (AOO) of the species is estimated to be <4 km 2, which meets criterion B2 under the Critically Endangered (CR) category of the IUCN Red List Categories and Criteria ( IUCN, 2019). Because the species grows on rocks beside a national highway, it is threatened by the annual maintenance and cleaning of road buffers, and its habitat will probably be threatened by road extension in the future. Based on current information (one location with projected decline in extent and quality of habitat, and AOO <4 km 2), the new species is provisionally assessed as Critically Endangered B2ab(iii).

Additional specimen examined. BHUTAN. Punakha: Toedpisa, Menchuna , 2285 m, 27 ix 2020, P. Gyeltshen 065 ( THIM) .