Tupistra thangii N. Tanaka & D.D.Nguyen, 2022

Nguyen, Danh Duc, Nguyen, Van Canh & Tanaka, Noriyuki, 2022, Tupistra thangii (Asparagaceae), a new species from southern Vietnam, Phytotaxa 552 (4), pp. 267-273 : 268-271

Tupistra thangii N. Tanaka & D.D.Nguyen , sp. nov.

Differs from the most similar species T. clarkei mainly by its wider leaves, upright or ascending spike, smaller flowers, perianth dark purple on both sides, laterally strongly revolute perianth lobes, and stamens adnate to the subbasal portion of the lobes.

Type:— VIETNAM. Lam Dong Province: Bao Lam District, Loc Bao Commune , around point 11°44’16.8”N 107°42’08.4”E; flat areas to steep slopes along river valley at elevation 800–900 m a.s.l.; very humid, primary to secondary broad-leaved forest mixed with bamboo; terrestrial herb with leaves to 1.5 m long in acidic soil rich in silicates, rarely on shady wet rocks, common locally; 18 December 2021, Nguyen Danh Duc & Nguyen Van Canh 2021493 (holotype VNMN).

Description:— Plant terrestrial, herbaceous, rosulate, rhizomatous, glabrous, perennial. Rhizome ascending to erect, usually unbranched, terete, stout, dirty brown, 7–15 cm long, 2.5–3.5 cm in diameter, covered with brown, coriaceous, partially disintegrated remnants of cataphylls and leaf sheaths. Roots sparse, almost straight or curved downward from near base, cord-like, fleshy, 2–6 mm in diameter, covered throughout with light brown root hairs. Stem erect, 2–6 cm long, enclosed by distichous conduplicate leaf sheaths and cataphylls. Cataphylls straight, ensiform or narrowly triangular, conduplicate, light grassy green, turning white in proximal half with age, 10–20 cm long, (1.5)2.5–4(6)cm wide (at base when flattened), basal portion abruptly widened up to 6 cm wide, soon becoming dry, coriaceous and almost brown, withering earlier than foliage leaves. Leaves (4)6–10(12), erect, arcuate or distally pendulous, basally equitant, (0.8)0.9–1.6(1.8) m long; blade narrowly elliptic to oblanceolate, (40–)50–60(–70) cm long, (5)7–18(20) cm wide (at the widest portion), wavy, leathery, uniformly dark green, glossy, midvein prominent abaxially, gradually tapering to thick, rigid, canaliculate petiole-like base (10–)15–30(–40) cm long, apex acute to shortly acuminate. Peduncle arising from leaf axil in distal part of stem, erect, oblique or almost horizontal, straight or ascending, slightly thickened upward, obscurely angled longitudinally, naked, fleshy, rigid, erect and reddish green at early anthesis, becoming curved and white at late anthesis, elongating with age; 7–10 cm long at early anthesis, 10–15 cm at late anthesis, and 20–30 cm after anthesis (or in fruit), 6 mm in diameter. Inflorescence (excluding peduncle) a dense spike, many-flowered, upright or ascending, 10–15 cm long, 3–3.5 cm in diameter; rachis obscurely and irregularly multi-angled longitudinally, fleshy, pinkish, turning green at late anthesis, portions from which flowers arise slightly concave. Bracts borne directly on rachis, 2 per flower, scarious along margins; outer bract located 2–3 mm below flower base, cucullate, obscurely rectangular, rather fleshy, white or light green, 4–6 mm long and wide, truncate to acute at apex, after anthesis becoming dry, brown and coriaceous; inner bract (bracteole) located lateral to flower, ovate to rectangular, light greenish, 3–4 mm long, 2.5–3 mm wide, apically acuminate, antrorse. Flower buds obliquely spheroidal or oblate, external side of perianth lobes dull whitish green with purplish rims. Flowers sessile, actinomorphic (or slightly zygomorphic), 1.2–1.6 cm across; Perianth 6-parted, broadly campanulate, dull dark purple to reddish purple, fleshy, with 6 white longitudinal stripes which correspond to decurrent portions of staminal filaments; proximal tube cup-like, 2.5–3.5 mm high, 5–7 mm in diameter; distal lobes broadly ovate, laterally strongly revolute (hence lobes look narrowly triangular), 6–8 mm long, 5–7mm wide. Stamens 6, opposite to perianth lobes; filaments adnate to subbasal portion of perianth lobes, shortly subterete, fleshy, 0.3–0.5 mm long, 0.4–0.6 mm in diameter, white, portions adnate (decurrent) to the perianth tube white; anthers dorsifixed, elliptic or broadly ovate, concavo-convex, pale yellowish, introrse, 1.4–1.6 mm long, 1.2–1.4 mm wide; pollen yellow. Pistil 1, straight (horizontal) or slightly ascending, 11–13 mm long; ovary superior, shortly subterete or oblate, later becoming ovoid, 1.2–1.8 mm long, 2–2.5 mm wide, glossy, cream white, turning green at late anthesis; style cylindric, white to pale yellow, 9.5–11.2 mm long, (0.5)1.3–1.5(1.6) mm in diameter; stigma peltate with nearly flat top, 2- to 7-lobed, each lobe somewhat irregularly dentate-crenate, white to pale yellow, turning pale brown with age, frontal surface papillulate, 3–5 mm in diameter.

Fruiting scape descending or curved downward, but distal part of infructescence ascending. Immature fruit globular, fleshy, dark green, ca. 3 cm in diameter, verruculose, normally 2-seeded; seeds ellipsoid or ovoid, ivory or off-white in color.

Etymology: —The specific epithet honors Hoang Minh Thang who is a Vietnamese gardener and the first discoverer of this new species.

Habitat and conservation status: — Tupistra thangii occurs on the floor of a primary to secondary evergreen broad-leaved forest mixed with bamboo at elevations 800– 900 m. Approximately 100 mature plants of this species were found in an area of 1 km 2 along a stream. They usually grew terrestrially on flat or steep locations, but sometimes also on shady wet rocks. The soil was rich in silicates and acidic. The habitat area as a whole, including its biotic and abiotic elements, appears not particularly endangered or damaged by human activities such as deforestation, but may be partially disturbed by grazing and/or trekkers’ camping. Since our data on the distribution and ecological aspects of this species are still very limited, we assign the species to the category “Data Deficient (DD)” in IUCN (2022).

Distribution: ―Currently known only from the type locality in Lam Dong Province, southern Vietnam.

Phenology: —Flowering in November–December. Fruiting: Only immature green fruit has been seen. Judging from the states of ripening fruit in May ( Fig. 1J ) and December ( Fig. 1I ), full ripening may require at least one year and a few months after fertilization ( Tanaka 2010a).

Taxonomic relationships:— Tupistra thangii is most similar to T. clarkei Hooker (1892: 325) from eastern Nepal and northeastern India ( Tanaka 2010a), for it shares (broadly) campanulate flowers with ovate or broadly ovate, slightly recurved lobes, perianth tubes internally dark purple with six white longitudinal stripes, and peltate stigmas with a dentate-crenate margin. However, it differs from the latter mainly by its wider (up to 20 vs. 11 cm) leaves, upright or ascending (vs. descending) spike, smaller flowers (1.2–1.6 vs. 1.5–2.5 cm in diameter), perianth dark purple on both sides (vs. pale dull yellowish brown except internally dark purple perianth tube), laterally more strongly revolute perianth lobes, stamens adnate to the subbasal (vs. basal) portion of perianth lobes, and whitish (vs. purplish) stigma. The new species is also similar to T. natmataungensis Y.H. Tan & H.B. Ding in Ding et al. (2019: 137) described recently from western Myanmar in sharing campanulate flowers, internally white-striped, dark purple perianth tube, whitish peltate stigma, etc. It is, however, distinguished chiefly by its ascending or erect (vs. creeping) rhizome, wider (to 20 vs. to 3.8 cm) leaves, much longer (7–15 vs. 1–1.6 cm at anthesis) peduncle, much longer (10–15 vs. 5.1–6 cm), ascending (vs. nearly horizontal) spike, numerous (vs. 3), smaller (1.2–1.6 vs. ca. 2.7–3.2 cm in diameter), aerial (vs. epigenous) flowers, abaxially dark (reddish) purple (vs. pale yellow orange) perianth, laterally more strongly revolute perianth lobes, stamens arising from the subbasal (vs. basal) portion of perianth lobes, and 2- to 7-lobed (vs. 3-lobed) stigma.

It is quite a unique trait that these three species possess an internally white-striped, dark purple perianth tube. Interestingly, this trait is also shared by other species having a pendulous spike such as T. fungilliformis F.T.Wang & S.Yun Liang in Wang & Tang (1978: 249) and T. tupistroides ( Kunth 1850: 319) Dandy (1932: 329) ( Tanaka 2010a) . Since most other species of Tupistra ( Tanaka 2010a) and all species of Rohdea ( Tanaka 2010b) have an upright or ascending spike, the pendulous spike is deemed as an advanced or specialized state (i.e. apomorphy) originated from the upright or ascending spike (plesiomorphy). In this respect, T. thangii is viewed as retaining a more primitive state than T. natmataoungensis with an almost horizontal spike and T. clarkei and some other species (e.g. T. fungilliformis ) with a pendulous spike. As these species are considered to be monophyletic, sharing a white-striped purple perianth as a synapomorphy, the ancestor of T. thangii is likely to have been deeply associated with the evolution of species with such non-ascending spikes. It is also of interest that T. thangii , T. clarkei and T. natmataoungensis are far apart in distribution in spite of their presumed phyletic proximity. This disjunctive distribution may not only reflect the past long-distance migration of this plant group, but also implies close historical connections between the floras of the Central Highlands of southern Vietnam, eastern Himalayan region and western Myanmar.

The present discovery of Tupistra thangii in southern Vietnam has largely extended the known range of this genus in eastern Indochina (e.g. Averyanov & Tanaka 2012, Averyanov et al. 2015, Tanaka et al. 2018) southward. This suggests that new members of Tupistra may still be found by further floristic expeditions in regions between Lam Dong Province and the northern regions of Vietnam.

Figures

FIGURE 1. Tupistra thangii. A. Habit in situ. B. Flowering plant (at late anthesis). C. Flowering scape at early anthesis. D. Flower buds. E. Flowering spike. F. Close up of flowers. G. Spike at late anthesis. H. Portion of spike at late anthesis. I. Fruit, external view and crosssection. J. Plant bearing young fruit. K. Floriferous plant flattened for preparation of holotype (Nguyen Danh Duc & Nguyen Van Canh 2021493). All photos taken by Nguyen Danh Duc: photo ‘J’ in May 2021, all others in December 2021.