Aschistanthera phucanhensis C.W.Lin, K.S.Nguyen & D.B.Tran, 2025

Phung, Van Khoa, Lin, Che Wei, Kieu, Thi Duong, Tran, Duc Binh, Nguyen, Quang Huy & Nguyen, Khang Sinh, 2025, Aschistanthera phucanhensis (Melastomataceae, Sonerileae), a new species from Phu Canh Nature Reserve, Hoa Binh province, Northwest Vietnam, Phytotaxa 682 (3), pp. 281-287 : 285-286

Aschistanthera phucanhensis C.W.Lin, K.S.Nguyen & D.B.Tran , sp. nov. ( Figs. 1 & 2 )

Type: — VIETNAM. Hoa Binh province: Da Bac district, Phu Canh Nature Reserve, Doan Ket commune, evergreen broad-leaved forests on sandstone mountain, around point N20.93278o E105.03889o, 900−1,000 m, 22 December 2023, K. S. Nguyen, D. B. Tran, PC-DB 15 (Holotype: HN 000076371!, isotype: HN 000076372!).

Diagnosis: Aschistanthera phucanhensis exhibits morphological affinities with A. cristanthera , yet differs by its hirsute-hispid (vs. glabrous) adaxial leaf surface, where the inner one or two pairs of lateral veins diverges from the midrib above of the base (vs. veins diverged from the base), hypanthium and sepals covered with red hirsute-hispid or gland-tipped hirsute-hispid hairs (vs. glabrous), and the anther ventral cleft is cordate (vs. totally absent).

Sub-caulescent herbs, 20–25 cm tall, lithophytic. Stems unbranched, apically ascending and proximally appressed to substrate and rooting at nodes, brown, 3–8 cm long, 0.5–1 cm in diameter, stout, knotty from leaf scars, densely covered with retrorse, rust-coloured or brown strigose; internodes congested. Leaves 5–10, decussate, isophyllous; leaf blades ovate to widely ovate, (5.5–)9.5–14 × (3.5–) 6–10 cm, chartaceous, base cordate, apex acute, obtuse or attenuate to shortly acuminate, margins crenulate or repand, with rows of very sparsely hispid trichomes ca. 0.5 mm long, venation acrodromous, 7–9-suprabasal, marginal pair diverged from the base and the inner veins symmetrical at the union with midvein, the innermost pair diverging 3–13 mm from the leaf base, a second pair produced 5–20 mm from the first pair, veins impressed or slightly raised on the adaxial surface, and prominently raised on the abaxial surface, tertiary 11–16 pairs, transverse tertiaries 20–32 pairs, conspicuous; adaxially dark green, ceraceous, slightly bullate between veins, sparsely hirsute-hispid; abaxially pale green, densely pink retrorse appressed-strigose on midrib, becoming white, erect and shorter towards the secondary and tertiary veins. Petioles 6.5–13 cm long, ca. 3 mm in diameter, sub-terete, densely covered with pink to reddish-brown retrorse appressed-strigose and glands or minutely gland-tipped trichomes. Bracts ca. 3 mm long, lanceolate, margin ciliate. Inflorescences terminal, thyrsoid, dusky pink to greyish-red, becoming reddish-yellow to yellowish-green towards the summit; 12–21 cm long, with red hirsute-hispid and sparsely minutely brown glands; peduncle 11.2–19 cm long, terete, apex with a 0.3–0.8 cm long rachis, paraclades with 2 to 4 flowers, often with extra branches sometimes absent, produced lower, 0.3–4.5 cm from the summit of peduncle, bearing 1 or 2 flowers. Flowers 4-merous; pedicels 5–7 mm long, covered with minutely reddish-brown glands and very sparsely red hirsute-hispid or gland-tipped hirsute-hispid; bracteoles narrowly triangular, 0.8–1.5 mm long or smaller. Hypanthium campanulate, creamy white to greenish-white, 8-ribbed, ca. 3 × 4 mm (calyx tube and lobes excluded), covered with minutely reddish-brown glands and sparsely red hirsute-hispid or gland-tipped hirsute-hispid. Calyx lobes 4, persistent, very widely triangular, measuring 1–1.5 mm long from the apex to the free portion, covered with red hirsute-hispid, gland-tipped hirsute-hispid and minutely reddish-brown glands externally; apex rounded, connate into a torus, each lobe with an green, acute-angled triangular external tooth, tipped by a red hispid. Petals 4, oblique, glabrous, widely oblong, elliptic-oblong to obovate-oblong, 8–14 × 7–10 mm, pinkish-white tinged rosy pink toward apex, apex mucronate-apiculate. Stamens 8 isomorphic, filaments slightly flat, 4–5 mm long, white, anthers quadrilocular, lanceolate, cordate at base, narrowing towards apex, slightly curved ventrally, ca. 3 mm long, golden yellow, pore 1, ventrally inclined; connective thick and raised into a ridge, rounded in cross section, with a well-developed, slightly flat beak-like dorsal spur of 0.5–0.8 mm long. Style 6–7 mm long, filiform, white, glabrous, stigma minutely capitate. Ovary 4-locular, ca. ⅔ as long as the hypanthium (crown excluded), adnate to the ovary proximally and free from the ovary distally for 1–1.3 mm; crown of four connate lobes with minutely red gland-tipped trichomes on margin; placentas axile, stalked. Capsules on pedicels 8–10 mm long, cupuliform, sub-quadrangular, 8- ribbed, 5–6 × 6–7 mm, crown slightly exceeding hypanthium, enlarged, slightly thickened, margin denticulate; top of capsule inside crown very thin, placental column distally entire, placentas non-thready.

Distribution and habitat: —Currently known only from the type locality, Da Bac district, Hoa Binh province, North Vietnam. Aschistanthera phucanhensis grows on humid sandstone rocks in the middle of the mountain slope covered by evergreen broad-leaved forest, between. 900–1,000 m elevation.

Etymology: —The specific epithet refers to Phu Canh Nature Reserve in Northwest Vietnam, where the new species was discovered.

Proposed IUCN conservation status: —A short field survey along the trail of 3–4 km long within the Phu Canh Nature Reserve, we encountered ca. 20 mature plants growing on soil or rock in the area of ca. 50 m 2. The habitat of Aschistanthera phucanhensis is strictly protected by regional authorities from any artificial disturbance. More field expeditions to catalog this species are needed to accurately assess its sub-populations. Therefore, its conservation status is tentatively assessed as “Data Deficient” (DD) according to the Guidelines for using the IUCN Red List categories and criteria, version 16 ( IUCN 2024).

Note: —The new species, Aschistanthera phucanhensis ,is characterized by several unique diagnostic morphological characters, including petioles bearing retrorse hairs and quadrilocular anthers with a conspicuous connective forming a ridge in cross-section. Morphologically, it closely resembles the sole previously known species of the genus, A. cristanthera , while conforming to nearly all of Hansen's (1987) defining characteristics for Aschistanthera . These traits clearly distinguish it from other related Asian genera within the tribe Sonerileae , such as Styrophyton and Phyllagathis s.l., thereby firmly supporting its placement within Aschistanthera .

The discovery of this second species within the genus provides an opportunity to refine its diagnostic characterization. Key characters now include petioles with retrorse hairs, a thyrse with lax, displaced branches, 4-merous flowers, isomorphic stamens, anthers with a conspicuous connective forming a ridge in cross-section and bearing a pointed dorsal spur while lacking ventral appendages, and a capsule with a membranous apex enclosed within crown lobes. Furthermore, this genus was previously only known from Kon Tum province, the central highlands of South Vietnam, this study confirms its distribution extends about 750 km to Northwest Vietnam (Hoa Binh province) ( Fig. 3 ).

Figures

FIGURE 1. Aschistanthera phucanhensis C.W.Lin, K.S.Nguyen & D.B.Tran. A. Habit. B. Detail of adaxial surface of the leaf blade. B'. Detail of abaxial leaf blade. C. Portion of petiole. D. Portion of peduncle. E. Bract. F. Flower in front view. F'. Flower in side view. G. Hypanthium. H. Longitudinal section of ovary. I. Stamens, side, dorsal and ventral views. I' Anther ventral view. I'' Anther side view. I'''. Anther dorsal view. J. Style. K. Portion of crown lobe, showing margins gland-trichomes. L, M. Gland-tipped hirsute-hispid and hirsutehispid. N. Glands. O. Longitudinal section of a mature capsule.

FIGURE 2. Aschistanthera phucanhensis C.W.Lin, K.S.Nguyen & D.B.Tran. A. Habit and habitats. B. Habit. C. Portion of stem. D. Petiole. E. Peduncles. F. Portion of leaf adaxial surface. G. Portion of leaf abaxial surface. H. Inflorescences. I. Flowers, front, side and back views. J. Longitudinal section of ovary. K. Anthers, ventral, side and dorsal views. L. Immature capsule, side and front views. M. Opened hypanthium, also showing stamens and style. N. Old-age capsule. O. Vertical section of an old capsule.

FIGURE 3. Distribution map of Aschistanthera phucanhensis (yellow star) and A. cristanthera (pink circle) in Indochina (The map is modified from https://geocat.iucnredlist.org/editor).