Boesenbergia monophylla N.S.Lý, N.G.Cao & Škorničk., 2025

Lý, Ng ọc-Sâm, Cao, Ng ọc-Giang & Leong-Škorničková, Jana, 2025, Boesenbergia monophylla (Zingiberaceae: Zingibereae), a new species from Central Vietnam, Phytotaxa 694 (2), pp. 184-192 : 185-190

Boesenbergia monophylla N.S.Lý, N.G.Cao & Škorničk. sp. nov., ( Figs. 1 & 2 )

Diagnosis: —In Vietnam, B. monophylla is similar to Boesenbergia quangngaiensis in flower shape and colour pattern of the labellum, but differs from it as well as from all other congeners in Cambodia, Laos and Vietnam by its monophyllous leafy shoots. In the rest of the distribution range, B. monophylla is most similar B. prainiana in monophyllous leafy shoots, but differs by dark green leaf blades with velvety appearance (vs. bright green shiny leaf blades), petioles as long or longer than ½ of the length of the leaf blade (vs. petioles short, not exceeding 1/4–1/3 of the length of the leaf blade), inflorescence largely hidden and not exceeding basal half of the petiole (vs. inflorescence fully exserted and exceeding petioles), and flowers pale-yellow with labellum ornamented with red central bands at basal half, widening and turning pink distally all the way to the margin (vs. flowers pure white with labellum ornamented by red-patched central bands at basal 2/3, widening and bright red all the way to the margin).

Type:― VIETNAM. Quang Ngai Province, Son Tay District, Son Lap Commune, Ta Ngam 1 Village , Mount Azin , 14°52’23.35”N, 108°24’46.06”E, elev. 732 m, 24 April 2020, Lý Ngọc Sâm Lý-1531 (holotype VNM (inclusive flowers preserved in spirit); isotypes P, SING) .

Evergreen, perennial, rhizomatous herb 27–40 cm tall, forming small, loose clumps with 2–5 leafy shoots per clump. Rhizome with numerous elements developing from the base of the previous element, oblong, 2–3.5 × 0.9–1.2 cm, externally dark-purple to almost black when young, turning brown with age, internally (in cross-section) with two concentric rings, the outer brown, inner dark-purple, non-aromatic, covered with red-purple, triangular scales, 0.5–1.1 cm long, with sparse long hair, soon decaying; roots many, fleshy, 10–20 × 0.3–0.4 cm, externally brown, internally dark-purple, covered with short fibrous roots. Leafy shoot with only 1 leaf per shoot (very rarely 2), 1.5–3.5 cm apart; bladeless sheaths tubular, 2.2–6.5(–8.9) cm long, ca. 1.5 cm wide, purple when young, striate, pubescent, turning brown and papery with age (striation more prominent with age and in dry material); leaf sheaths light green, slightly striate, with scattered long and soft white hairs (margin opaque whitish-green); ligule hardly visible, hidden below sheathing bracts, bilobed, lobes ovate, 1.5–2.5 mm long, translucent white, pubescent; petiole stout, 6–15 cm long, shallowly canaliculate, green, sparsely long and soft white hairs; leaf blade broadly ovate to elliptic-ovate with sides unequal in width, 13.3–22 × 6.5–11 cm, weakly plicate, adaxially dark green, with velvety sheen, glabrous, abaxially dull greenish-white, long and soft white hairs, apex short, acute, base rounded, slightly unequal, margin glabrous throughout including apex. Inflorescence central, clasped between the leaf sheath and bladeless sheath, 5.5–9 cm long, basipetalous with usually only a single flower open a time; peduncle 0.5–1.5 × 0.3–0.4 cm, whitish or greenish, with sparse long and soft white hairs; spike narrowly ovate to fusiform, dorso-ventrally pressed, 4.5–7.8 cm long, 1–1.6 cm at the widest point, longitudinally furrowed on the flowering side, composed of distichously arranged bracts facing both in one direction and rachis exposed on the non-flowering side (inflorescence V-shaped in cross-section); sterile bracts 2, narrowly ovate, 1.4–3 cm long, 0.7–1.1 cm at widest point, purple or dull translucent white, with sparse long and short white hairs, margins translucent white, apex short acute; fertile bracts 8–14 per each spike, the bracts in each rank 0.5–1 cm apart, narrowly ovate, open to the base, 15–31 × 4–6 mm, purple or dull translucent white, with sparse soft white hairs, each enclosing a single bracteole and a single flower; bracteoles open to the base, ovate-elliptic, 29–33 × 8–13 mm, purple or dull translucent white, externally with sparse soft white hairs, apex 2 or 3-toothed (teeth ca. 0.5 × 1 mm), margins overlapping and fully enclosing the floral tube. Flower 3.8–5.6 cm long; calyx tubular, 5–6 × 1–1.5 mm, white, externally with sparse soft white hairs, with a unilateral incision ca. 4 mm, apex with 2 conspicuous, short, obtuse lobes; floral tube 3.4–4.8 mm long, 1.5–2 mm diam. at base, widening gradually to 2.2–2.5 mm diam. at widest point at apex, mostly white, gradually transiting to pale yellow distally, glabrous; dorsal corolla lobe oblong, 15–17 × 4–5.5 mm, semi-translucent pale yellow with translucent veins and margins, glabrous on both sides, apex cucullate, often revolute; lateral corolla lobes oblong, 14–16 × 4–4.5 mm, semi-translucent pale yellow with translucent veins and margins, glabrous, apex slightly cucullate; androecial cup oriented ca. 100˚ to the floral tube, ca. 3 × 2.5 mm wide, externally white with glandular hairs, internally bright red at part connected to the labellum, with scattered glandular hairs; labellum oriented ca. 75˚ to the apex of the bract, obovate to broadly obovate, 2–2.7 × 1.8–2.2 cm, basal part with sides curved upwards and overlapping with staminodes, pale yellow to cream white with deep bright red band in the basal half, somewhat extending to upper half and transiting to wider dark pink patch in the middle (pink extending all the way to the margin), densely covered in glandular hairs on both sides, apex emarginate, undulate, flexing outward; lateral staminodes obovate, 16–16.5 × 6.5–7 mm, pale yellow with translucent veins, slightly reflexed distally, densely covered in glandular hairs, apex round or truncate. Stamen 12–14 mm long; filament 4–5 × 1.2–1.5 mm, white, glabrous; anther 7.5–8 × ca. 2 mm, connective tissue cream white to pale yellow, with some glandular hairs; anther crest absent; anther thecae ca. 8 × 1 mm (each), dehiscent throughout their entire length, white; pollen white. Ovary cylindrical to barrel-shaped, 4–5 × 1.2–1.5 mm, trilocular, white with reddish tinge at apex, glabrous; style filiform, 3.4–5.4 cm long, white, with sparse glandular hair; stigma shallowly cup-shaped, ca. 1 × 0.5 mm, white, ostiole circular, glabrous; epigynous glands 2, linear, 5.5–6 mm long, ca. 0.5 mm in diam., cream white. Fruits and seeds not seen.

Etymology:― The Greek-derived specific epithet “ monophylla ” refers to the leafy shoots mostly consisting of only a single leaf.

Vernacular name & uses: —Bồng nga truật một lÁ (Vietnamese, proposed here); single-leaved Boesenbergia (English, proposed here). No uses were reported by locals.

Ecology & phenology: — Boesenbergia monophylla grows on stream banks and shady areas in secondary evergreen broad-leaved forests, at elevations of 700–900 m a.s.l. Flowering was observed in May–June, and fruiting is estimated to extend to July or August.

Distribution & IUCN preliminary assessment:— So far known only from Son Tay district in Quang Ngai Province ( Fig. 3 ). Currently only two populations of about 150 clumps of fertile plants were observed in Son Lap and Son Mau communes in Mount Azim. Of these, a single population of around 50 clumps of mature plants was found in Son Lap Commune, while four colonies comprising approximately 100 clumps of mature plants were sighted in Son Mau Commune. The extent of occurrence (EOO) and the area of occupancy (AOO) were estimated to be ca. 46.7 km 2 and 24 km 2 respectively. Although this area is under the protection of the local authorities of the Department of Forest Protection , the area has no legal status as a National Park or Nature Reserve. Although no uses were reported by the local people, there is a high-risk potential due to loss of the habitat within its range, as vast forested land continues to be cleared for Acacia plantations. Based on currently available data we therefore propose to treat this species provisionally under the category of Endangered (EN B1, B2b (i,ii,iii), D) according to the IUCN Red list criteria ( IUCN 2022). Further survey work in the areas adjacent to Son Tay district is necessary to assess the distribution and conservation status of this species more accurately.

Additional specimens examined (paratypes):― VIETNAM. Quang Ngai Province, Son Tay District, Son Lap Commune, Ta Ngam 1 Village , Mount Azin , secondary evergreen broad-leaved forests, Lý Ng ọc Sâm Lý-1529, Lý- 1530, Lý-1532 & Lý-1535 ( VNM) ; Son Mau Commune, secondary evergreen broad-leaved forests, near stream bank, Lý Ng ọc Sâm and Cao Ng ọc Giang Lý-1541 ( VNM), Cao Ngọc Giang Cao-005 & Cao-007 ( NIMM) .

Notes: ―In the present study, the number of Boesenbergia species in Vietnam is raised to seven, viz. B. parvula (Wall. ex Baker 1890: 218) Kuntze (1891: 685) , B. petiolata Sirirugsa (1987: 423) , B. quangngaiensis N.S.Lý , B. rotunda ( Linnaeus 1753: 2) Mansfield (1958: 239) , B. siphonantha (King ex Baker) M.Sabu, Prasanthk. & Škorničk. ( Baker 1890: 222, Sabu et al. 2004: 55) and B. xiphostachya (Gagnep.) Loes. ( Gagnepain 1906:147, Loesner 1930: 568). Of these, only the newly described B. monophylla and B. quangngaiensis are evergreen, retaining their leafy shoots throughout the year, while the remaining five species undergo dormancy. B. siphonantha produces either lateral inflorescence arising directly from the rhizome near the stem base or a central inflorescence arising in between the leaf sheaths while the other six species only have central inflorescence. Among the species with a central inflorescence, B. petiolata and B. rotunda have a spike clasped by the uppermost leaf sheaths while B. parvula , B. quangngaiensis , B. xiphostachya and B. monophylla produce an elongated spike, mostly exserted from the leaf sheaths. A key to all seven Boesenbergia species in Vietnam is given below.

Flowers of C. monophylla are very similar to that of B. quangngaiensis ( Lý 2017a) in terms of colours and pattern on the labellum, but its monophyllous habit combined with a dark green velvety leaf blade distinguish it readily from B. quangngaiensis and any other Boesenbergia species in Vietnam. In sterile stage, or with inflorescences but absence of fresh flowers, this species, is more likely to be misidentified as a member of Distichochlamys Newman (1995: 65) .

Figures

FIGURE 1. Boesenbergia monophylla. A. Flowering plants in natural habitat. B–D. Close-up of the flowers: top view (B), front view (C) and side view (D). From the type Lý Ngọc Sâm Lý-1531. Photos by N.S. Lý.

FIGURE 2. Boesenbergia monophylla. A. Flowering plant with rhizome and roots. B. Inflorescence enclosed in a bladeless sheath (left), inflorescence and bladeless sheath separated (right). C. Basal part of the plant with rhizome, roots and cross-section of rhizome and root. D. Dissection of a flower (from left): Flower, bract, bracteole, calyx, floral tube with ovary, calyx and stamen attached, dorsal and lateral corolla lobes (upper row), lateral staminodes and labellum (lower row); E. Details of ovary with epigynous glands and stamen in front, back and side views. From the type Lý Ngọc Sâm Lý-1531. Photos by N.S. Lý.

FIGURE 3. Distribution map of Boesenbergia monophylla (solid circle).