Begonia wiformis T.S.Hoang & C.W.Lin, 2023

Hoang, Thanh Son & Lin, Che-Wei, 2023, A new species Begonia wiformis, and a new record of B. filiformis (B. sect. Coelocentrum, Begoniaceae) from nothern Vietnam, Phytotaxa 591 (4), pp. 292-300 : 292-299

Begonia wiformis T.S.Hoang & C.W.Lin , sp. nov. § Coelocentrum ( Figs. 2 , 3 & 4 )

Type:— VIETNAM. Lang Son Province, Bac Son District, Tran Yen Commune , 21°41’42”N, 106°22’31”E, 563 m elev., growing in cracks of mossy rocks on semi-shaded limestone cliffs in evergreen broad-leaved forest., 18 March 2022, Hoang Son 4251 (Holotype VAFS; Isotype VNMN) .

Diagnosis:— Close to B. langsonensis C.-I Peng & C.W.Lin in its subglabrous laminae, bracts with a denticulate margin and zygomorphic androecium. It differs in having a stoloniferous growth habit (vs. rhizome not elongated), stipules with a ciliate margin (vs. entire), the upper surface of the lamina with a velvety texture (vs. waxy texture) and maculation (vs. uniformly green), pistillate flowers 3 or 4 tepals (vs. only 3 tepals) and capsule with semi-persistent (vs. caducous) tepals.

Monoecious herb, rhizomatous initially and becoming stoloniferous. Rhizome creeping, reddish-brown, ca. 1 cm thick, internodes 4–10 mm long, sending out stolons to 60 cm or longer, 2.5−4 mm thick, villous or subglabrous, internodes 1.5−5 cm long. Stipules semi-persistent, reddish-brown, ovate-triangular to very widely triangular, 7–10 × 3.5–5 mm, herbaceous, keeled, glabrous, margin ciliate to fimbriate, apex apiculate, arista 2–4 mm long; stipules of stolon similar to rhizome but smaller. Leaves alternate, petiole terete, brownish-red to crimson, 7−25 cm long, 2.5−5 mm diameter, glabrous or sparsely villous; leaf blade asymmetric, oblique, ovate to wide ovate, 7.5−13 × 4.3–7 cm, broad side 2.7–5 cm wide, basal lobes cordate, 2.2–4.1 cm long, apex attenuate to acute, margin subentire with a line of appressed puberulous hairs; leaf thick chartaceous, succulent, adaxially malachite green, blackish-olive green to maroon, variegated with silver grey to greyish-green zones or semicontinuous patches along main veins, sometimes with irregular silvery dots between veins, with a brownish-red or green patch at junction on lamina and petiole, venation green toward base, sometimes blue iridescence; abaxially pale green to magenta, glabrous or very sparsely minutely puberulous; venation basally ca. 8 palmate, midrib distinct, ca. 2 secondary veins on each side, other primary veins branching dichotomously or nearly so, tertiary veins reticulate; leaves of stolon widely to very widely ovate, occasionally polygonal, 3.3–6 × 2–4.5 cm, margin subentire, ciliate, apex obtuse to acute. Inflorescences axillary, bisexual, cymose, arising directly from rhizome, 2 or 3 orders of branching; peduncle reddish, 3.2–19 cm long, glabrous. Bracts caducous, pinkish to pale brownish-red, at basal node of inflorescence ovate, ca. 10 × 8 mm, glabrous, margin denticulate; bracts of upper inflorescence similar but smaller. Staminate flower: pedicel rosy pink to red, 1.3–2.2 cm long, glabrous, tepals 4, rosy pink to pinkish-white, glabrous, outer 2 suborbicular to very widely ovate, 10–14 × 12–16 mm, margin entire, apex rounded, inner 2 oblanceolate, 10–17 × 2.5–4 mm, apex obtuse or rounded; androecium zygomorphic, 4–5 mm across; stamens golden yellow, 25–35; filaments ca. 1.3 mm long, fused at base; anthers obovate, ca. 1.8 mm long, 2-locular, apex rounded. Pistillate flower: pedicel pink to red, 8–15 mm long, glabrous, tepals 3 or 4, pinkish-white to rosy pink, glabrous, outer 2 widely orbicular to very wide obovate, 10–14 × 11–18 mm, margin entire, apex rounded, inner 1 or 2 oblanceolate, 5–10 × 1.7–3.5 mm, apex obtuse to rounded; ovary trigonous-ellipsoid, 6.5–10 mm long, 2.5–4 mm thick (wings excluded), pink to yellowish-pink, glabrous; 3- winged, wings unequal, pink, subglabrous, margin entire; lateral wings narrower, narrowly crescent-shaped, 3–4 mm wide, abaxial wing crescent-shaped, 4.5–7.5 mm wide; ovary 1-locular with intruded parietal placentation, placentae 3, bilamellate; styles 3, shortly fused at base, golden yellow, ca. 4–5 mm long, stigma spirally twisted. Capsule tepals semi-persistent; capsule trigonous-ellipsoid, 8.5–14 mm long, 3.5–5. mm thick (wings excluded), greenish when fresh; wings unequal, 11–16 mm long, lateral wings 3–6 mm wide, abaxial wing triangular, 5–8 mm wide, truncate to rounded distally, truncate to cordate proximally.

Distribution and ecology:— Endemic to Tran Yen Commune, Bac Son District, Lang Son Province, Vietnam. Growing in cracks of mossy rocks on semi-shaded limestone cliffs in evergreen broad-leaved forest, elevation ca. 560 m.

Etymology:— Wiformis (W-shaped), referring to the shape of its maculation somewhat similar with the letter "W" in the upper surface of lamina.

Conservation status:— A small population of the new species is distributed in an area of about 1 km 2, which is not included in any protected forest, so that it may be threatened by Begonia collectors. According to IUCN (2019), the species may be listed as DD (Data Deficient). Future botanical surveys are needed for a complete conservation assessment of the species.

Notes:— Begonia wiformis can be recognized by its rhizomes that send out elongate stolons, subglabrous leaves with velvety texture above, bracts with a denticulate margin and zygomorphic androecium. In its geographical distribution and morphological characters, the new species is most closely related to B. langsonensis C.-I Peng & C.W.Lin ( Peng et al., 2015) but it differs in sufficient characters to be considered a distinct species. Begonia yizhouensis D.K.Tian, B.M.Wang & Y.Tong ( Tong et al., 2019) is probably another closely related species, with both species sharing several similar morphological characters such as ciliate stipules, glabrous upper leaf surface that is variegated, glabrous tepals and zygomorphic androecium. However, the new species cannot be mistaken for B. yizhouensis , which has a stoloniferous rhizomes (vs. only rhizome), leaf texture velvety (vs. waxy), stipules reddish-brown (vs. whitish-green), petiole glabrous or sparsely villous (vs. densely hirsute-villous), capsule abaxial wing truncate to cordate proximally (vs. cuneate) and flowering around May (vs. November to December). Among the rhizomatous begonias on limestone karsts in Sino-Vietnamense, B. wiformis is also superficially similar to B. pseudodryadis C.Y.Wu ( Wu & Ku, 1995) and B. pseudodryadis var. bitepala Aver. ( Averyanov et al., 2020) in having ovate, velvety leaves and 4-tepaled staminate flowers, however, B. wiformis differs in having bracts with a denticulate margin (vs. entire), zygomorphic androecium (vs. actinomorphic) and pistillate flowers with 3 tepals (vs. 5).

Figures

FIGURE 2. Begonia wiformis T.S.Hoang & C.W.Lin.A. Habit; B, B'. Portion of leaf, upper and lower surfaces; C. Stipule; D, D'. Bracts; E, E'. Staminate flower, face and side views; F, F'. Stamens, ventral and dorsal views; G, G', G''. Pistillate flower, face and side views; H, H'. Style and stigmatic band, dorsal and ventral views; I. Capsule; J. Cross section of ovary.

FIGURE 3. Begonia wiformis T.S.Hoang & C.W.Lin. Plants photographed in the type locality to show variably colorful foliage. A. Stoloniferous growth habit; B–I. Rhizomatous growth habit.

FIGURE 4. Begonia wiformis T.S.Hoang & C.W.Lin. A. Habits; B. Various complex foliar maculation patterns on upper surfaces; C. Stipules on rhizome, D. stipules on stolon; E, F. Portion of leaf, upper and lower surfaces; G. Inflorescence; H, I. Bracts; J. Staminate flower; K. Pistillate flowers; L. Capsules; M. Cross section of ovary.