Truongsonia A.J.Hend., N.S.Lý, W.J.Baker, S.Bellot, J.Dransf., & Eiserhardt, 2023

Sâm, Lý Ng ọc, Baker, William J., Bellot, Sidonie, Dransfield, John, Eiserhardt, Wolf L. & Henderson, Andrew, 2023, Truongsonia (Arecaceae: Arecoideae: Truongsonieae) - a new palm genus and tribe from Vietnam, Phytotaxa 613 (3), pp. 201-212 : 202-207

Truongsonia A.J.Hend., N.S.Lý, W.J.Baker, S.Bellot, J.Dransf., & Eiserhardt , gen. nov.

Type:— Truongsonia lecongkietii N.S.Lý, W.J.Baker & A.J.Hend.

See description under species.

Truongsonia lecongkietii N.S.Lý, W.J.Baker & A.J.Hend. , sp. nov. Type:— VIETNAM. Quang Ngai Province: Tra Bong district , precise locality withheld, primary tropical evergreen forests, elev. 640 m asl., 14 May 2020, Ngọc-Sâm Lý, Lý-1521 (holotype: VNM!, isotype: NY!)

Diminutive, acaulescent, clustering (rarely solitary), unarmed, monoecious, pleonanthic palm to 1 m. Stems forming dense clumps, 10–15 cm long, 1.5–2 cm diameter, positively geotropic, “saxophone” type ( Tomlinson 1990), subterranean or horizontal, brown, densely covered with stout roots, with short and obscure internodes 2–5 mm long. Leaves 9–15 in crown, reduplicate, not exceeding 1 m; sheaths 10–15 cm long, splitting open to the base, persistent, smooth, yellowish-brown, with caducous indumentum of brown, matted,fimbriate hairs, with flimsy, early disintegrating ligules 2.5–6 cm long, ligules bearing linear, brown hairs; petioles 50–66 cm long, smooth, with caducous indumentum as sheath, shallowly channeled, green adaxially, paler green abaxially; rachises 20–44 cm long, with scattered, brown indumentum ad- and abaxially, with a filamentous, distal extension beyond the leaf blade to 40 cm long; leaf blades entire-bifid, (14.5–) 19–77 cm long, 10–12.4 cm wide at the apex of rachis, attenuate at the base, bifid for 22–31 cm at the apex, green adaxially, glaucous-green with scattered, caducous indumentum abaxially, glabrous adaxially, with 6–10 main veins on each side of rachis, prominent adaxially, corresponding to lamina plications, leaf apices with splits 6–15 mm deep. Inflorescences 40–43 cm long, interfoliar, slender, erect initially, protandrous, branched to 1 order; prophylls 2.0– 2.5 cm long, ca. 0.7 cm wide, tightly sheathing, bicarinate, truncate, opening and eroding apically; peduncles 26–31 cm long; peduncular bracts 3–4, tubular, slender, tightly sheathing, the proximal splitting and disintegrating apically, the distalmost peduncular bract to at least 33 cm long, splitting distally for one third its length to form a ca. 18 mm wide cowl over the rachillae before drying and becoming pendulous, light green, with scattered indumentum; rachises 2–8 cm long; rachillae 5–10, 11–16 cm long, 0.5–1.0 mm diameter at anthesis, 1.0– 1.4 mm diameter in fruit, radiating from the rachis at anthesis, subtended by minute rachis bracts, puberulous, sometimes with scattered, long, brown hairs; flowers in triads proximally, paired or solitary staminate distally, alternately to spirally arranged along the rachillae, each borne superficially in a shallow recess in the rachilla, pale yellow at anthesis, subtended by minute rachilla bracts; floral bracteoles minute; staminate flowers sessile, obovoid, asymmetric, 2–2.5 mm long, 1.5–1.8 wide; sepals 3, not united, imbricate, 1–1.2 mm long, 0.7–0.8 mm wide (in bud prior to anthesis), ovate, cucullate, keeled at the base abaxially, tanniniferous along distal margin; petals 3, united in lower third, valvate, 2–2.5 mm long, 0.8–1.6 mm wide, obovate, cucullate; stamens 6, biseriate, united at base, outer, antesepalous whorl presented below the inner, antepetalous whorl; outer filaments ca. 0.5 mm long, inner filaments ca. 1 mm long; anthers 0.6–0.7 mm long, 0.6–0.7 mm wide, globose, connective black-brown, dorsifixed, latrorse; pistillodes 0.6 mm long, 0.6 mm wide, conical, trilobed; pistillate flowers sessile, subglobose, 1.5–1.7 mm long, 1.5–1.6 mm wide (in bud prior to anthesis); sepals 3, not united, imbricate, 0.7–1.0 mm long, 1.3–1.5 mm wide, broadly triangular, cucullate, keeled at the base abaxially, tanniniferous along distal margin; petals 3, not united, imbricate, 1.3–1.5 mm long, 1.4–1.6 mm wide, broadly ovate, cucullate; ovary triovulate-tricarpellate, ovoid, ca. 1.5 mm long, ca. 1 mm wide, stigmas tightly adpressed (in material seen), trilete, with 3 locules at base, each containing 1 ovule; staminodes not seen; fruits 17.9– 18.2 mm long, 7.5–8.4 mm diameter, oblong-ellipsoid, smooth, bright red, with basal stigmatic residue; mesocarp 1.3 mm thick; seeds 1 per fruit, 14.5–14.7 mm long, 5.8–6.1 mm diameter, oblong, basally attached; endosperm homogeneous; embryo lateral. ( Figs. 1–5 ).

Distribution:— VIETNAM. Central Vietnam, Truong Son Range (Dãy Trường Sơn), Quang Ngai Province: Tra Bong district. Known only from the type locality, where a small population of 10–15 plants were seen scattered in less than 500 ha of forest.

Habitat and phenolgy:—This species grows in moist, shady, understorey vegetation on steep slopes near streams in primary, evergreen, broad-leaf forest at about 600–700 m elevation. Truongsonia has been observed in flower and fruit in May.

Vernacular names (Vietnamese language):—Cau lê công kiệt (coined here).

Uses:—None recorded. The new species has potential as an ornamental plant due to its small habit and beautiful leaf shape.

Conservation status:—Critically Endangered (CR B1B2ab(i-v), D; IUCN 2012). The extremely small population size of this species immediately qualifies it for the highest extinction risk. Although this species is under the protection of the local authority and the Department of Forest Protection of Tra Bong District, Quảng Ngãi province, its habitat is frequently disturbed by human activities such as harvesting of non-timber forest products, logging and clearing of the forest for Acacia plantations. Further exploration of adjacent areas is necessary to understand the extent and population sizes of this species better.

Etymology:—The genus name is derived from the Truong Son Range, Dãy Trường Sơn, in Vietnamese. The species is named for Associate Professor Lê Công Kiệt, University of Natural Science, Vietnam National University in Ho Chi Minh City, in honour of his long-time contribution to Vietnamese botany.

Specimens examined:— VIETNAM. Quang Ngai Province: Tra Bong district, precise locality withheld, elev. 640 m asl., 14 May 2020, Ng ọc-Sâm Lý , Lý-1521 (holotype: VNM!, isotype: NY!), elev. 618 m, 15 May 2020, Ngọc-Sâm Lý, Lý-1525 (K!), elev. 687 m, 15 May 2020, Ngọc-Sâm Lý, Lý-1527 (P!) .

Figures

FIGURE 1. Truongsonia lecongkietii. Habit. A, B. Habit in the wild. C. Uprooted plant showing stem with saxophone growth. Photos: N.S. Lý.

FIGURE 2. Truongsonia lecongkietii. Vegetative morphology.A. Leaf, abaxial surface, showing fibre-like extension of the rachis through the sinus of the two leaf lobes. B. Leaf, adaxial surface. C. Leaf sheath, abaxial surface. D. Base of clump. E. Petioles, showing dry, fibrous, disintegrating ligules. Photos: N.S. Lý.

FIGURE 3. Truongsonia lecongkietii.Inflorescence morphology.A.Entire inflorescence.B. Distal part of inflorescence showing rachillae and peduncular bract. C. Base of plant showing insertion of inflorescence. D. Rachillae bearing young fruit. Photos: N.S. Lý.

FIGURE 4. Truongsonia lecongkietii. Flowers and fruit. A. Rachilla with floral triads and open staminate flowers. B. Open staminate flower. C, D. Fruit whole and in section (ruler with mm scale). Photos: N.S. Lý.

FIGURE 5. Truongsonia lecongkietii. A. Rachilla. B. Floral triad with one open staminate flower. C. Floral triad, one staminate flower removed. D. Staminate flower bud. E. Open staminate flower bud in longitudinal section. F. Staminate petal. G. Staminate sepal. H. Androecium. I, J. Staminate flower in two views. K. Pistillate flower bud. L. Pistillate petal. M. Pistillate sepal. N. Gynoecium in two views. O. Ovary in transverse section, showing 3 locules, each with 1 ovule. P, Q. Fruit whole and in longitudinal section, showing lateral embryo. R. Detail of basal stigmatic remains on fruit. S. Seed. Scale bar: A, P, Q, S = 7 mm; B, C, I, J = 1.6 mm; D–H, K–O = 1.25 mm, R = 2.5 mm. All from Ngọc-Sâm Lý, Lý-1521 (NY). Drawn by Lucy T. Smith.