Rohdea dangii K.S.Nguyen, N.Tanaka & Aver., 2021

Nguyen, Khang Sinh, Tanaka, Noriyuki, V. Averyanov, Leonid, Nguyen, Phuong Hanh & Tran, Duc Binh, 2021, Rohdea dangii (Asparagaceae), a new species from northwestern Vietnam, Phytotaxa 482 (1), pp. 65-72 : 68-70

Rohdea dangii K.S.Nguyen, N.Tanaka & Aver. sp.nov. ( Figs. 1 & 2 )

It differs from the most closely related species, R. tonkinensis , mainly by the significantly longer, thicker rhizome, non-sheathing amplexicaule leaf blades, half-terete peduncle, much shorter bracts mostly not exceeding the flowers, and crateriform perigone tube.

Type:— VIETNAM. Son La Province: Quynh Nhai District, Muong Giang Commune , remnant primary evergreen broad-leaved forest on limestone mountains, in middle of steep slopes at elevation of 1190 m a.s.l., around point 21.63377° N 103.55414° E. Terrestrial or lithophytic perennial herb about 50–100 cm long, stem prostrate and erect, flower green then turning yellowish, fruits reddish orange, locally common, 6 March 2019, Nguyen Sinh Khang & Vi Van Dang, NSK 1163 (holotype HN!, isotype HN!, LE 01067230 !, http://en.herbariumle.ru/?t=occ&id=13445) .

Herb terrestrial or lithophytic, monopodial, glabrous, evergreen, perennial. Rhizome prostrate, fleshy, cylindrical, (40–)50–70(–95) cm long, (1.2–)1.5–1.7(–1.9) cm in diameter, externally greenish grey, brown, or light orange, internally white or cream, with many annular leaf scars irregularly spaced at intervals of (0.3–)1.2–2.5(–3.5) cm, bearing (somewhat loose) tufts of (2–)3–5(–9) adventitious roots at intervals of (5–)7–10(–12) cm. Roots cordlike, (2) 3–4 mm in diameter, fleshy, velutinous. Stem ascending, nearly erect, cylindrical, (7–)15–25(–31) cm long, (1.3–)1.4–1.8(–2) cm in diameter, brown or light orange, bearing (6–)7–13(–16) leaves. Cataphylls 2–3 at base of peduncle, suberect or oblique, narrowly deltoid or lanceolate, acuminate or aristulate, (4–)4.5–6.5(–7) cm long, (1.5–)2–3(–3.5) cm wide at base, laterally involute, margin membranous, with numerous longitudinal veins, subcoriaceous, pale green, later turning yellowish green to brown and scarious. Leaves spreading or suberect when young, becoming deflexed with aging, oblanceolate or narrowly elliptic, (18–)20–25(–28) cm long, (4–)4.5–5(–6.5) cm wide, tapering to petiolelike base (3–)4–5(–6) cm long and (0.9–)1.2–1.3(–1.5) cm wide (when flattened), basal dilated portions amplexicaule but not imbricate (thus not forming sheath), apex acuminate or aristulate, medially slightly canaliculate toward base, adaxial surface green, abaxial surface paler, somewhat glossy on both sides, midrib adaxially impressed, abaxially raised, secondary veins numerous, parallel, closely spaced at intervals of (1.5–)2–2.5(–3) mm, slightly raised on both sides, margins entire, somewhat undulate. Peduncle half-terete, 2.5–5.5 cm long, (0.4–)0.5–0.6(– 0.7) cm wide, distally bracteate; sterile bracts on peduncle (0–)1–2(–3), oblique, deltoid to broadly ovate, dilated at base, nearly entire or shallowly undulate, acuminate or acute, distally often longitudinally concave, 4–5 mm long, 3.5–4.5 mm wide at base (when flattened). Inflorescence a spike of ca. 30–45 flowers, cylindrical, 4–5 (–6) cm long, (1.6–)1.7–1.8(–1.9) cm in diameter, flowers densely spirally arranged, forming 5 longitudinal rows; rachis fleshy, 5-angulate. Floral bracts 2 per flower, borne directly on rachis, white with green tint, pale green or yellowish green, subcoriaceous, margins irregularly undulate, membranous, whitish; outer bract borne shortly below flower, ascending, somewhat cucullate, concave, deltoid, with U- or V-shaped base, apex obtuse to acute or acuminate, (3–)4–5(–6.5) mm long, (2–)3–4(–5) mm wide at base (when flattened), distal bracts longer than proximal ones, distally inflexed, mostly shorter than flowers; inner bract (bracteole) borne lateral to flower, very small, sometimes reduced to tiny scale, flat to moderately concave, deltoid to subulate, usually acuminate to acute, rarely obtuse, (0.3–)0.5–1.5(–2) mm long, (0.5–)1–1.5(–2) mm wide (at base). Flowers (nearly) actinomorphic, hermaphroditic, sessile, borne on shallow pits between ridges on rachis, almost horizontal, some distal ones facing slightly upward; perigone crateriform, distally 6-cleft, (6.5–)7–9(– 9.5) mm in diameter, fleshy, green, turning yellow to (dull) orange at late anthesis; perigone tube (proximal syntepalous part) broadly crateriform, (1.5–)1.8–2.3(–2.5) mm long, (4–)4.5–5.5(–6) mm in diameter; perigone segments often obliquely ascending, triangular ovate to triangular oblong, (4.5–)5–5.5(–5.8) mm long, (2.5–)2.8–3.2(–3.5) mm wide, margins entire, green, with numerous tiny white dots scattered on both surfaces, distally acuminate with usually incurved unguiculate apex 0.5–0.7 mm long, outer three broader than inner three, basally not imbricate, medial portion of abaxial side usually angulate. Stamens 6, arising from near base of perigone segment; filaments subterete, distally strongly incurved, (1.1–)1.2–1.3(–1.4) mm long, (0.4–) 0.5– 0.6 mm in diameter, somewhat bullate dorsally, lower decurrent portions dilated and incrassate, 1.3–1.5 mm thick including the wall of perianth tube, proximally green, distally greenish or whitish; anthers dorsifixed, biloculate, introrse, orbicular ovate, retuse at upper and lower ends, 0.8–0.9(–1) mm long, 1–1.2 mm wide, facing downward, white with brownish tint. Pistil 1, tricarpellate, superior, erect, 2.5–2.8(–3) mm long; ovary ovoid, (2.4–) 2.5– 2.7 mm long, 2.5–2.8(–3) mm broad (at lower middle broadest portion), glabrous, sparsely scattered with white minute dots, 3-locular; ovules 4 per locule, biseriate and nearly collateral on axial placentae, anatropous, ca. 0.5 mm long; style inconspicuous, broadly conoid, 0.3–0.5(– 0.6) mm long, 0.6–0.8(–1) mm in diam.; stigma positioned nearly as high as base of filaments, trisected, (0.9–)1–1.3(–1.4) mm across, each segment oblong-elliptic, 0.4–0.6 mm long, 0.3–0.5 mm wide, horizontal or slightly ascending, surface papillulate, margin more or less involute. Fruits berry, ellipsoid, 1.5–1.7 cm long, 1–1.1 cm wide, pericarp fleshy, surface brightly reddish orange and glossy, 1-seeded. Seeds ellipsoid, 11–12 mm long, 8–9 mm wide, glossy, brownish white.

Paratype:― VIETNAM. Dien Bien Province: Muong Cha District, Hua Ngai Commune, Ha La Chu Village , highly degraded, humid primary evergreen broad-leaved forest on very steep slopes of remnant mountains composed of solid limestone at elevation 1100–1400 m a.s.l., around point 21°53ʹ46ʺ N 103°10ʹ17ʺ E. Terrestrial or lithophytic herb to 0.5 m tall on shady rocky slope, flower dull orange, common, 7 April 2011, L. Averyanov, P. K. Loc, N. Q. Hieu, N. T. Vinh, CPC 1937 ( LE01050379 !, http://en.herbariumle.ru/?t=occ&id=3009) .

Etymology:―The specific epithet is named after Vi Van Dang, who greatly assisted the field survey and contributed to the discovery of the new species.

Habitat and phenology:― Rohdea dangii occurs as a terrestrial or lithophytic herb under the remnant primary evergreen broad-leaved forest covering steep slopes of limestone mountains at elevations 1100–1400 m a.s.l. The habitat area has a tropical monsoon climate with a dry winter (January, February, and December) and a rainy summer (May to July or August). In the area the mean annual temperature is reported as 21–23°C, the mean annual rainfall is 1612.7–1759.6 mm, and the mean annual relative humidity is 84% ( Nguyen et al. 2000). The plant flowers in March to April and ripens in April next year.

Distribution and conservation status:― Rohdea dangii is currently known only from two localities in northwestern Vietnam located ca. 50 km away from one another; one is Muong Giang Commune, Quynh Nhai District, Son La Province (habitat of holotype and isotypes), the other is Hua Ngai Commune, Muong Cha District, Dien Bien Province (habitat of paratype). In the former habitat, approximately 25 individuals forming four clumps were observed in a small mountain that has long been subjected to agricultural activities and exploitation for timber and non-timber forest products. The vegetation there is accordingly highly degraded, as shown in Fig. 1A . In the latter habitat, the plant was common. However, our current knowledge on the overall abundance and distribution of the new species is still insufficient, hence the conservation status of the new species is assessed here as Data Deficient (DD) based on the guidelines presented in the IUCN Red List Categories and Criteria version 14 ( IUCN 2019). Further field surveys are needed to acquire a more accurate, adequate assessment of the conservation status of the new species.

Taxonomic relationships and morphological traits:―Sharing an elongate upright stem with no cataphylls (except for those at the base of peduncle), narrowly elliptic leaves, and incurved filaments of which the lower decurrent portions are conspicuously incrassate, Rohdea dangii is apparently most closely related to R. tonkinensis distributed in northern Vietnam and Yunnan and Guangxi in southwestern China ( Tanaka 2010). The new species is, however, easily distinguishable from the latter mainly by the somewhat softer, more fleshy, longer, more robust rhizome, reaching 95 (vs. 50) cm long and 1.9 (vs. 1.0) cm in diameter, thicker stem (up to 2 vs. 1.1 cm in diameter), amplexicaule but not sheathing (vs. shortly sheathing) leaf blades, half-terete (vs. terete) peduncle, significantly shorter bracts (3–6.5 vs. up to 45 mm long), crateriform (vs. subcampanulate) perigone tube with apically clawed (vs. acute) segments, and shorter filaments (1.1–1.4 vs. 2–2.5 mm long). The new species also somewhat resembles R. wattii , a wide spread species distributed in Vietnam, Bhutan ( Noltie 1994), India and China ( Tanaka 2010), in having a prostrate rhizome and aerial stem, but differs chiefly by the thicker stem (up to 2 vs. 1 cm in diameter) with no cataphylls (vs. 1–2 cataphylls at the base of every 2 to 3 annually developing consecutive leaves), half-terete (vs. terete) peduncle, cylindrical (vs. ellipsoid) spike, significantly shorter (3–6.5 vs. up to 20 mm long), abruptly acute (vs. tapering from base to apex) bracts, shorter (1.5–2.5 vs. 2.5–5 mm) perigone tube with apically clawed (vs. not particularly clawed) segments, and shorter filaments, pistils and styles. For more details see Table 1, where a comparison of several key traits between Rohdea dangii , R. tonkinensis , and R. watti is made. In having elongate aerial stems, R. dangii may also be somewhat similar to R. emeiensis described from Sichuan Province, China ( Zhu 1982). However, the latter is readily distinguishable from R. dangii by its much slender stem, fewer, smaller leaves, shorter peduncle, laxer spike of 6–9 flowers, and coroniform small laminas surrounding the orifice of perigone tube. Rohdea ensifolia described from Yunnan, China, also has an elongate aerial stem with no cataphylls ( Tanaka 2010), but this species markedly differs from R. dangii in having long narrowly linear leaves. Accordingly, these two species appear somewhat remotely related to each other.

Among the species of Rohdea , only R. dangii , R. tonkinensis , and R. ensifolia , are currently known to have stems bearing no cataphylls. Cataphylls are generally regarded as organs to protect internal young organs to develop (e.g., of leaves, stem, and/or flowers) from unfavorable natural conditions such as coldness and dryness in winter. All the three species are distributed in the southwestern periphery of the generic range, where a warmer climate prevails than in the central or northeastern part of the generic range (e.g. Sichuan and regions eastward such as Hubei in China and Japan). As earlier suggested for R. tonkinensis and R. ensifolia ( Tanaka 2010) , absence of cataphylls in the three species is deemed as an apomorphic state evolved as a consequence of adaptation to a warmer climate. Development of elongate aerial stems in the three species may also reflect the warm climate, under which plants can continue growing without being interrupted by severe climatic factors.

*Data on R. tonkinensis and R. watii were based on specimens cited in the “Appendix” and literature including protologues ( Clarke 1889, Baillon 1893, Tanaka 2010).

Figures

FIGURE 1. Rohdea dangii. A. Scenery of the type locality in Son La Province where R. dangii grows under primary evergreen broadleaved forest at middle and upper zones of limestone mountains; the forest is largely deforested especially in the lower part. B. R. dangii growing on limestone. C. Collector holding the plant. D. Habit. E. Part of rhizome with adventitious roots. F. Rhizome in cross section. G. Basal dilated portion of leaf blades amplexicaule but not imbricate (arrowed). H. Part of aerial stem bearing infructescence. I. Cataphyll, adaxial view. J. Leaf base, abaxial view. K. Abaxial side of leaf in part. L. Adaxial side of leaf apex. Photos and layout by K.S. Nguyen. Photographed plant corresponds to N.S. Khang 1163 (type material).

FIGURE 2. Rohdea dangii.A. Inflorescence. B. Longitudinal section of spike. C. Inflorescence (in spirit) cross-cut, view from below. D. Peduncle and its portions cross-cut. E. distal, middle and proximal outer bracts and sterile bract. F. Outer bract (pointed with red arrow) and bracteoles (blue arrows). G. Flower, front view. H. Partial flower, showing the interior. I. Perigone segment cut basally. J. Part of perigone with a stamen. K. Ovary cross-cut showing ovules in locules. L. Ovules borne on placenta. M. Seeds. Photos and layout by K.S. Nguyen. Photographed plant corresponds to N.S. Khang 1163 (type material).