Primulina hoangmongii K.S.Nguyen, Aver. & C.W.Lin

Nguyen, Khang Sinh, Averyanov, Leonid V. & Lin, Che Wei, 2024, Primulina hoangmongii (Gesneriaceae), a new species from northern Vietnam, Phytotaxa 645 (2), pp. 179-185 : 180-184

Primulina hoangmongii K.S.Nguyen, Aver. & C.W.Lin , sp. nov. ( Figs. 1 & 2 )

Type: — Vietnam, Yen Bai Province: Luc Yen District, remnants of primary evergreen broad-leaved forest at an elevation of 150–350 m a.s.l., lithophytic perennial herb, with very thick rhizome up to 10 cm long, not common, 22 February 2023, Hoang Van Mong s.n., cultivated in his garden, flowered on 15 January 2023, Hoang Van Mong & K.S. Nguyen, YB-LY 003 (holotype HN!) .

Diagnosis:— Primulina hoangmongii is well recognized by its suborbicular leaves, large, attractive, bright yellow flowers, and ligulate, entire stigma. It superficially resembles P. albicalyx B.Pan & Li H.Yang in Yang & Pan (2017: 312) with its broadly ovate rosette leaves, appressed to substrate, and light yellowish corolla. However, the new species clearly differs in its linear to narrowly-lanceolate bracts (vs. narrowly ovate to ovate) 8–12 × 2–3 mm (vs. 18–25 × 9–14 mm), green calyx (vs. white), rich yellow corolla (vs. pale yellowish), base of the upper lip flat, thin, and rich pure yellow (vs. swelling between lobes, yellow-brownish), and a ligulate, entire stigma (vs. deltoid, 2-lobed).

Description:—Herb lithophytic, perennial, rhizomatous, acaulescent. Rhizome subterete, creeping or ascending, very thick, simple of few branching, pale brown, up to 10 cm or longer, 7–21 mm in diameter, internodes congested. Leaves 6–12, petiolate, opposite, decussate, congested at the apex of rhizome; petiole light green, up to 4.5 cm long, 5.5–8 mm in diameter, transversely elliptic in cross section, slightly grooved adaxially, densely puberulous or hirsute with white hispid hairs; leaf blade succulent, suborbicular or broadly ovate, 8–12 × 7–10 cm, adaxially grassy green, puberulous with appressed whitish or light brownish strigose hairs, abaxial surface light green to almost white, strigose and puberulous, with dense hispid hairs along veins, apex rounded to obtuse, at base rounded to subcordate, sometimes slightly decurrent, margin entire, slightly down recurved, lateral veins 4–6 on each side of median vein, flat or slightly impressed adaxially, prominent abaxially. Cymes 1–4 or more on one stem, axillary, often 2-flowered, flowers sweet fragrant; peduncle pale green, 4–7 cm long, ca. 2 mm in diameter, densely puberulous or hispid with white hairs; bracts linear to narrowly-lanceolate, 8–12 × 2–3 mm, puberulous and hispid on both side, bracteoles similar to bracts but smaller; pedicel 3–3.5 cm long, ca. 1 mm in diameter, puberulous. Calyx 5-partite to the base; lobes equal, narrowly lanceolate or narrowly triangular, 10–13 × 1.8–2.5 mm, green, puberulous abaxially, sparsely puberulent adaxially, apex acuminate, margin entire. Corolla 5–6 cm long, 10–12 mm in diameter at the mouth, rich yellow, with 5 longitudinal maroon stripes; outside puberulous and shortly hispid, inside puberulent; tube tubular, 2.5–3 cm long, ca. 7 mm in diameter at the middle, tube slightly upright, at base gradually constricted to 3 mm in diameter; limb distinctly 2-lipped; adaxial lip 2-lobed to over the middle (almost two third of its length), slightly obliquely ovate to crescentshaped, rounded at apex, 9–12 × 10–17 mm; abaxial lip 3-lobed to about middle, lateral ones slightly obliquely spathulate to oblong, 12.5–16 × 10–15 mm, central one spathulate, rounded at apex, 12.5–17 × 11–19 mm. Stamens 2, adnate 15–18 mm above the tube base, filaments white, with longitudinal, maroon streaks on ventral side; ca. 15 mm long, twisted at lower third, sparsely hairy with translucent glandular hispid hairs, more dense in the upper half; anthers pale yellowish to almost white, fusiform to ellipsoid, 3–4 × 1.5–2 mm, glabrous; staminodes 3, translucent to white, glabrous, lateral ones adnate to 11–13 mm above the tube base, filiform, 5–7 mm long, apex capitate; the central one adnate to 4–5 mm above corolla tube base, ca. 1.5 mm long. Disc annular, pale yellow, ca. 1 mm in height, margin entire. Pistil 2.5–3.5 cm long, ovary light green, cylindric, 13–18 mm long, 1.6–1.8 mm in diameter, densely puberulous with hispid translucent glandular hairs; style 10–15 mm long, ca. 1 mm in diameter, light green, densely puberulous with hispid translucent glandular hairs; stigma ligulate, yellowish-green, ca. 3 mm long, 1–1.2 mm wide, adaxially verruculose, apex rounded, base attenuate. Capsule not seen.

Distribution and ecology:— Primulina hoangmongii is currently only known from its type locality in the Luc Yen District of Yen Bai Province (the central part of northern Vietnam). It grows on shaded vertical rocks or steep slopes of karstic limestone hills covered by evergreen broad-leaved forest at elevations of 150–350 meters above sea level. The plant flowers in late December until early February.

Etymology:— The species epithet refers to the name of its discoverer, Mr. Hoang Van Mong.

Vernacular name:— Báo xuân hoàng mộng.

Proposed IUCN conservation status: —The new species is currently only found in 3 close locations of Luc Yen District. Its extent of occurrence (EOO) and area of occupancy (AOO) are currently estimated as less than 100 km 2 and 10 km 2, respectively. According to available data, the number of mature plants observed in the wild is not more than 100 individuals. The distribution range of this species is not covered by any protected area, and Primulina species are widely collected for ornamental purpose. In such conditions, assuming a single location (sensu IUCN) and severe threats, the new species is preliminarily assessed as Critically Endangered (CR) B1ab(ii,iii,v) + B2ab(ii,iii,v). Nevertheless, as for other newly described taxa with an almost punctiform or very limited distribution, provisionally assessed as CR (e.g., Wagensommer & Venanzoni 2021, Zavatin et al. 2023), it will be necessary collecting further data on distribution, population size, and threats, and defining the appropriate strategies for the long-term conservation of the species.

Similar taxa:— Morphologically, this new species exhibits obvious distinctions from all known Vietnamese Primulina species. In its overall morphology, the new species somewhat resembles P. albicalyx found in Guangxi (SE China), but surely differs in several characters indicated in the diagnosis. It also exhibits some affinities with P. swinglei ( Merrill 1918: 156) Mich.Möller & A.Weber in Weber et al. (2011: 785) in its few-flowered cymes with small, linear bracts and pistil with a ligulate, entire stigma. However, significant disparities exist between the three species mentioned, such as lamina texture as well as corolla size and color. A detailed comparison of the three Primulina species is provided in Table 1 .

Note:— Primulina hoangmongii stands out as one of the most captivating species of Gesneriaceae in Vietnam, possessing high horticultural potential because of its succulent, glaucous leaves arranged into compact rosettes alongside its large, attractive, rich yellow, fragrant flowers.

Figures

FIGURE 1. Primulina hoangmongii K.S.Nguyen, Aver. & C.W.Lin. A. Habit. B, B'. Portion of leaf, adaxial and abaxial surfaces. C, C'. Bracts, C''. bracteole. D. Flower, front view. E. Dissected and flattened corolla, showing stamens and staminodes. F. Stamens. G. Staminodes. H. Calyx lobes. I. Pistil. J. Stigma. All drawn from the holotype, Hoang Van Mong & K.S. Nguyen, YB-LY 003 by Che-Wei Lin.

FIGURE 2. Primulina hoangmongii K.S.Nguyen, Aver. & C.W.Lin. A, B. Habitat and habit. C. Flattened flowering plant. D. Portion of leaf, adaxial surface, showing densely appressed strigose or puberulous. E. Portion of leaf, abaxial surface. F. Corolla, front view, view from above, and side views. G. Bracts and bracteoles. H. Stigma. I. Basal portion of pistil, disc and calyx lobes. J. Dissected and flattened corolla, showing stamens and staminodes. K. Pistil and calyx, also showing cross section of ovary. L. Stamens. M. Staminodes. Photos A–B by H.V. Mong, in the locus classicus (Yen Bai Province), C–M by K.S. Nguyen, from specimen used for preparation of the holotype, Hoang Van Mong & K.S. Nguyen, YB-LY 003. Photo correction and design by K.S. Nguyen.