Raphiocarpus bicallosus C.H.Nguyen, Aver. & F.Wen, 2023

Nguyen, Cuong Huu, Wen, Fang, Pham, Toai Minh, Nguyen, Yen Thi, Bui, Thanh Minh, Bui, Doi The, Nguyen, Khang Sinh & Averyanov, Leonid V., 2023, The checklist of Raphiocarpus species (Gesneriaceae, Didymocarpinae) in the flora of Vietnam with the description of a new species, R. bicallosus, Phytotaxa 616 (3), pp. 223-234 : 225-229

4. Raphiocarpus bicallosus C.H.Nguyen, Aver. & F.Wen , sp. nov. ( Fig. 1 , 2 & 3 )

Diagnosis:—The new species is closely related to R. tamdaoensis , but differs from it in the presence of distinct prophylls (vs. prophylls absent), a 3–5-flowered inflorescence (vs. inflorescence 1-flowered), a dark purple-brown corolla limb (vs. limb pale yellow), the presence of 1 staminode and 2 hairy bosses inside the tube (vs. staminode absent, the tube without ornamentation), as well as a glabrous ovary, and capsule 5–6 cm long (vs. ovary densely velutinous, capsule less than 4 cm).

Type: — VIETNAM. Thanh Hoa: Thuong Xuan District, Bat Mot Commune , Xuan Lien Nature Reserve , 300– 500 m, 20°3′6″N 105°7′22″E, 24 November 2021, H. C. Nguyen NHC 20211124004 (holotype VNF!, isotypes LE01170317 !, LE01170318 !) .

Etymology:—The specific epithet bicallosus is derived from Latin bi - (two) and callosus (having calli), referring to two prominent, elongate, hairy bosses inside the corolla tube placed at the base of the abaxial lobe.

Description:— Perennial herb 40–50 cm tall. Stem prostrate, ascending to erect, branching, rooting throughout the plagiotropic part, leafy with opposite leaves and prophylls in the orthotropic portion, hairy when young, becoming glabrous with age. Prophylls commonly present at nodes in the lower, non-leafy part of the stem, almost sessile, 5–8 mm long, 4–6 mm wide, brown, hairy along main and secondary veins, finely serrulate and ciliate along the margin. Leaves petiolate; petiole 1–1.5 cm long, green to green flushed with purple, densely hairy with appressed brown hairs; leaf blade of each pair unequal, rarely equal, narrowly ovate to obliquely elliptic, 11–14 cm long, 5–6 cm wide, grassy green above, pale green, or pale green flushed with purple below, with sparse long stiff hairs 0.8–1 mm long on both surfaces, obtuse to almost rounded, oblique at base, acute or shortly acuminate at apex, serrate along the margin; adaxial midrib depressed, abaxial midrib distinctly protuberant; lateral veins in 5–7(8) pairs, distinct on both surfaces. Inflorescence axillary or subterminal dichasium with 3–5 flowers; all axes with sparse erect glandular hairs; peduncle 5–8 cm long; paired sterile bracts present at each dichotomous fork, free, ovate to elliptic, 4–8 mm long, with erect glandular hairs, margin entire, both surfaces pale green to purplish; petiole 6–10 mm long, densely hairy. Calyx with 5 almost free, broadly lanceolate to narrowly ovate lobes, 5–6 mm long, 2–3 mm wide, with erect glandular hairs outside, glabrous inside. Corolla tube outside yellow to orange-yellow, inside yellow with more or less dense brown purple spots, distally with 5 dark purple-brown lobes; tube obconoid, 3.2–3.6 cm long, 4–5 mm in diameter at the base, 1.2–1.5 cm wide in apical part, distinctly narrowing and slightly bent in lower third, with orifice 1–1.2 cm in diameter, sparsely covered with soft, erect glandular hairs outside, inside glabrous, except two hairy bosses below the base of abaxial lip; limb 1.6–1.8 cm in diameter, distinctly 2-lipped; adaxial lip 4–6 mm long, 8–9 mm wide, 2-lobed at apex, lobes sub-equal, nearly semi-circular; abaxial lip 6–8 mm long, 8–10 mm wide, 3-lobed, lobes sub-equal, broadly ovate, rounded at apex, lateral slightly oblique. Stamens 4, adnate to ca 7 mm above the base of the corolla tube, in two pairs, each pair coherent at their apices, anther thecae confluent; filaments glabrous, 20–22 mm long, adnate to the corolla tube ca 10 mm long, with free part 10–12 mm long, ca 1 mm in diameter; anthers ca 1 mm long and wide; staminode 1, ca 4 mm long, adnate to ca 4 mm above the base of the corolla tube. Disc pale yellowish green, annular, obscurely 5-lobed, 1–1.3 mm tall. Pistil 3.2–3.4 cm long; ovary narrowly cylindrical, glabrous, 2–2.2 cm long, about 1.5 mm in diameter; style narrowly cylindrical, 1.2–1.4 cm long, sparsely pubescent, about 1 mm in diameter; stigmas 2-lobed, lobes ovoid to almost globular. Capsule green when young, glabrous, 5–6 cm long, about 3 mm in diameter, narrowly cylindrical, almost straight, net twisted, loculicidally dehiscing from the apex to the base.

Ecology and phenology:—It grows in primary and old secondary lowland, evergreen, broad-leaved forests at elevation of 300–500 m a.s.l., commonly along streams and on stream valley slopes in wet rocky places with soil rich in humus. Flowers in September–November; fruits in October–December.

Distribution:—It is endemic to Vietnam known from a single location in Thanh Hoa Province (Thuong Xuan District).

Conservation status:—Available observations indicate that the species meets the following IUCN (2023) Red List criteria: only one population is known with an extent of occurrence that cannot be calculated, the area of occupancy is less than 10 km 2 (B2a), and the decline is expected for the area, extent, and quality of habitat (iii) and the number of mature individuals (v). Following these conditions, the species conservation status may be tentatively estimated as Critically Endangered, CR B2a(iii,v)b(iii,v).

Notes:— Raphiocarpus bicallosus is somewhat similar to R. tamdaoensis ( Phuong et al. 2012) in its plant habit and ecology. Both plants have creeping stems, ascending and erect distally, similar characteristics of the indumentum of the stem and leaves, as well as similar shapes of the leaf blade, calyx, and pistil. Both species are also found in humid evergreen broad-leaved forests on damp soils, commonly along wet stream slopes. At the same time, our plant occurs on soils derived from granite parental rocks at elevations of 300–500 m a.s.l., while R. tamdaoensis inhabits rhyolite mountain slopes distinctly higher, with elevations of 800–1300 m a.s.l. Morphologically, new species can be easily distinguished from R. tamdaoensis by having prophylls (vs. prophylls absent), 3–5-flowered inflorescence (vs. inflorescence 1-flowered), dark purple-brown corolla limb lobes (vs. corolla limb lobes pale yellow), the presence of one staminode and two prominent hairy bosses inside the tube (vs. corolla tube inside without hairy ornamentations, staminodia absent), glabrous ovary (vs. ovary densely velutinous), and glabrous capsule 5–6 cm long (vs. capsule pubescent, 3–4 cm long). It is remarkable that two bosses densely covered with long, stiff hairs placed inside the corolla tube. This is a unique character that distinguishes our species from all its congeners and is reflected in its epithet. Comparative morphological characters between two species are presented in Table 1 .

Figures

FIGURE 1. Raphiocarpus bicallosus. A. Intact flowering shoot. B. Flattened plant parts. C, D. Internodes and prophylls. E. Leaf petiole. F. Leaves, adaxial and abaxial side. G. Median part and margin of the leaf blade, adaxial surface. H. Peduncle. I. Young inflorescence. J. Intact inflorescences. K. Flower buds and flowers, side and half-side views. L. Calyx segments. M. Intact perianth, frontal view. N. Perianth tube, views outside and inside with details of stamens and staminodia. O. Pistil. P. Distal part of pistil and stigma. Q. Ripening fruit.All photos made from the plant used for the type preparation, NHC 20211124004. Photos, correction, and plate design by Cuong Huu Nguyen and L. Averyanov.

FIGURE 2. Raphiocarpus bicallosus. A. Habit. B. Leaves, adaxial and abaxial side. C, D. Internodes and prophylls. E. Flower buds and flowers, side and half-side views. F. Intact perianth, frontal view. G. Perianth tube, views outside and inside with details of stamens and staminodia. H. Calyx segments. I. Pistil and stigma. Drawn by Kien C.N. from the holotype NHC 20211124004.

FIGURE 3. Raphiocarpus bicallosus, holotype specimen, NHC 20211124004.