Begonia namkadingensis, Yang, Chen-Jui, Tagane, Shuichiro, Souladeth, Phetlasy, Okabe, Norikazu, Hu, Jer-Ming & Yahara, Tetsukazu, 2018

Yang, Chen-Jui, Tagane, Shuichiro, Souladeth, Phetlasy, Okabe, Norikazu, Hu, Jer-Ming & Yahara, Tetsukazu, 2018, Flora of Nam Kading National Protected Area III: Begonia namkadingensis (Begoniaceae), a new species in limestone area, Phytotaxa 334 (2), pp. 195-199 : 195-198

Begonia namkadingensis C.-J. Yang, Souladeth & Tagane, sp. nov. Fig. 1 .

Type:— LAOS. Bolikhamxay Province: Nam Kading National Protected Area, ca. 330 m elv., 18°10’N, 104°28’E, 30 June 2017, Tagane

S., Souladeth P., Okabe N. & Yang C.-J. L1202 (holotype: FOF!, isotypes: HAST!, HNL!, KYO! — a spirit collection, TAI! — a spirit collection).

Additional specimens examined:— same locality, 26 June 2017. Tagane S., Souladeth P., Okabe N. & Yang C.-J. L960 (FOF, KYO, TAI).

Begonia namkadingensis is clearly distinguished from the other previous known species in Laos and its surrounding countries by its small habit up to 17 cm long, 4–13 lanceolate leaves which alternate distichously arranged on the stem, 2 stigmas and 2-locular fruit. It is phenotypically most similar to B. pteridiformis of Peninsular Thailand in its tuberous habit, leaf arrangement on the stem, lanceolate leaf shape, and the morphology of its staminate flowers and pistillate flowers, but differs in its smaller habit (5–10(–17)) cm in B. namkadingensis vs. 12–25 cm in B. pteridiformis ), usually not branched stem (vs. 2–5 branched), fewer leaves per plant (4–13 vs. 8–30), smaller leaves (0.5–2.7 × 0.5–1.1 cm vs. 2–8 × 0.5–1 cm), its relatively sparse indumentum of glandular hairs on its stems and both sides of the lamina (vs. densely covered with glandular hairs on the whole plant), narrower inner dorsal tepals of pistillate flower (0.8–1 mm wide vs. 1–2 mm wide), fewer stamens (4–7 vs. 10–12) and smaller fruit (ca. 0.5 × ca. 0.4 cm vs. ca. 1.5 × 1–1.2 cm).

Monoecious herb, lithophytic on moist mossy limestone rocks, 5–10(–17) cm tall. Tubers small, subglobose, with fibrous roots, 1–3 mm in diameter. Stems succulent, 0.5–2 mm in diameter, strigose near base, almost glabrous on upper part; not branched, or rarely branched near base, dark red at base, pink to pale green toward shoot apex, more or less zigzag form, internodes 5–10 mm long. Stipules obovate to obovate-suborbiculate, 0.4–0.7 × 0.3–0.5 mm, membranous, margins serrate, with glandular hairs at apex of teeth. Leaves 4–13 per plant, basifixed, alternate, distichously arranged in a horizontal plane; petioles terete, 1–3.5 mm long, ca. 0.5 mm in diameter, pink to pale green, shortly strigose for lower leaves, glabrous for upper leaves; lamina membranous, slightly oblique to symmetric, 0.5–2.7 × 0.5–1.1 cm, upper leaves narrower and longer than lower ones, narrowly lanceolate to lanceolate, lower leaves ovate to lanceolate, acute at apex, rounded to truncate at base, margin serrate, with 4–7 teeth per side, adaxial surface green, with scattered small translucent triangular scales, abaxial surface pale green to white, or pale red to white, glabrous; venation palmate-pinnate, midrib clearly visible, pale green and slightly sunken adaxially, white to pale green and slightly prominent abaxially, lateral veins 3–6 pairs, obscure on adaxial surface, somewhat visible on abaxial surface. Inflorescence terminal and axial near the apex, to 3 cm long, 1–3 times branched with 1–4 staminate flowers and one pistillate flower per branch, protandrous, bracteate; peduncle 8–14 mm long, pale green to white, bracts and bracteoles membranous, triangular to orbicular-triangular, 0.2–1.6 × 0.5–2 mm, apex obtuse to rounded, margin serrate to dentate, with glandular hairs at teeth apex, pale green to white. Staminate flower: pedicel 5–8 mm long, white to pale green, glabrous or very sparsely covered with glandular hairs; tepals 4, white, margin entire, glabrous on both surfaces, outer 2, broadly elliptic to obovate, 2.5–3 × 2–2.5 mm, apex obtuse, base cuneate, inner 2, linear to narrowly oblanceolate, 2–3 × 0.8–1 mm; androecium zygomorphic; stamens 4–7, filaments ca. 1 mm long, fused at base, greenish yellow, anthers ca. 1.3 mm long, yellow. Pistillate flower: pedicel 3–4.5 mm long, white to pale green, sparsely covered with glandular hairs; tepals 5, white, margin entire, glabrous on both surfaces, outer 2, ovate to elliptic, 2–3 × 1.7–2 mm wide, inner 3 unequal, lateral ones wider, slightly oblique, narrowly elliptic, 2–3 × ca. 1.3 mm, dorsal one narrower, linear to narrowly lanceolate-elliptic, 2–3 × 0.8–1 mm; ovary trigonous-ellipsoid, 2–2.8 mm long, 1.5–2 mm in diameter, white, with glandular hairs near base, 3-winged, dorsal wing larger, sail-like, broader and truncate distally, ca. 1 mm tall, lateral wing present only at lower half of ovary, ca. 0.2 mm tall; styles 2, ca. 1.2 mm long, fused at base, yellow, stigmatic band C-shaped, papillose. Capsule pale green in vivo, nodding, horizontal with the dorsal wing downward, with persistent tepals, trigonous-ellipsoid to globose, ca. 5 mm long, ca. 4 mm in diameter (not including the wings and persistent tepals), two lateral wings slightly enlarged, ca. 1 mm tall, forming a half-bowlshape, dorsal wing enlarged, 2–3 mm tall; horizontal when mature, the ventral side of the ovary wall disintegrates and forms an upward facing opening. Seeds many, ellipsoid, ca. 0.8 mm long, brownish.

Distribution and ecology:— LAOS (Nam Kading National Protected Area). At present, Begonia namkadingensis is known only from the type locality. The species was collected on shaded moist mossy limestone rocks along a dried stream, accompanied by Argostemma lobbii Hooker (1880: 44) , A. siamense Puff (2009: 137) ( Rubiaceae ), Impatiens sp. ( Balsaminaceae ) and Epithema sp. ( Gesneriaceae ). Flowers and young fruits were collected in June.

Etymology:— This specific epithet namkadingensis refers to the type locality.

Vernacular name:—ສມກບນາກະດງ (Som Kop Nam Kading)

GenBank accession no.:— Tagane et al. L1202: LC318136 (rbcL) and LC318137 (matK).

Primary conservation assessment:— Endangered (EN) ( IUCN 2012). Only one population with around 100 fertile individuals was found in a restricted area of less than 100 m 2 along a stream in the protected area. Thus, we applied the status as EN according to the IUCN criteria D. The habitat is close to the road and vulnerable to disturbance by human activity, and the population appears to have been somewhat disturbed by road construction in recent years. The category may be elevated to Critical Endangered (CR) through continuous monitoring. However, more populations of B. namkadingensis may be found when as similar limestone habitats are explored in Nam Kading National Protected Area and its neighbor Phou Hin Poun National Protected Area. A long-termed monitoring program at the type locality and further field surveys of neighboring areas are necessary.

Notes:— Begonia sect. Parvibegonia comprises 33 species distributed from India to Indochina, and extending to Java ( Doorenbos et al. 1998, Hughes et al. 2015, Phutthai & Hughes 2017). Begonia namkadingensis has tuberous habit, alternate leaves, 2 stigmas in pistillate flower, 2-locular fruits with one enlarged wing, and bifid placenta. We tentatively classify this species in sect. Parvibegonia based on the morphology, but one reviewer suggested the new species should be placed in sect. Lauchea . Further studies would be necessary to clarify which section the new species should be within the genus.

The discovery of this species during our botanical survey in the Nam Kading National Protected Area, as well as many other new records and new species recently reported ( Souladeth et al. 2017, Tagane et al. 2018), suggests that more comprehensive field surveys in this protected area will result in the discovery of more new records and new species.

Figures

FIGURE 1. Begonia namkadingensis C.-J. Yang, Souladeth & Tagane. A. Habit; B. Plant lower surface; C. Staminate flower; D & F. Pistillate flowers (front view and lateral view, respectively); E. Cross section of ovary; G. Young fruit; H. Mature fruit.