Eriolaena bacgiangensis T. H. Bui, 2025

Tran, Van Tien, Tran, The Bach, Vu, Ha Phuong, Cao, Hoang Tuan & Bui, Thu Ha, 2025, Eriolaena bacgiangensis (Malvaceae), a new species from Vietnam, PhytoKeys 256, pp. 13-20 : 13-20

Eriolaena bacgiangensis T. H. Bui sp. nov.

Figs 1 , 2 , 3

Type.

Vietnam. • Bac Giang Province, Son Dong District, Huu San Commune , 21°23'26.1"N, 106°57'27.6"E, alt. 178 m, 18 July 2015, T. B. Tran, D. B. Tran, T. C. Vu, V. H. Do, H. Q. Bui, H. S. Doan, VK 6489 (holotype: HN 80497 !; isotypes: HN 80498 !, HN 80499 !, HN 80500 !, VNM 00074095 !) .

Diagnosis.

Eriolaena bacgiangensis is most similar to E. candollei due to the shape of the leaf blade, number of basal and lateral veins, presence of epicalyx in the flower bud, lanceolate epicalyx; shape of sepal (linear – lanceolate) and yellow petals. E. bacgiangensis differs from E. candollei by the pedicel length (1.4–2.3 cm), presence of epicalyx after flowers at anthesis, densely fringed epicalyx, style significantly exceeds staminal tube length and fruit apex round.

Description.

Small tree up to 8 m tall; branchlets stellate puberulent. Stipules caducous. Petioles 1.1–6.0 cm long, densely pubescent. Leaf blades cordate, 7.0–23 × 3.6–18.0 cm; apex acute to caudate; base shallowly cordate; surfaces pubescent; veins densely pubescent; stellate hairy, denser abaxially; margin obtusely dentate; basal veins 5–7; secondary veins 3–5 - paired. Inflorescence racemose, axillary to terminal, 3–10 - flowered, 13.0–18.0 cm long. Flower pedicels 1.4–2.3 cm long, densely pubescent. Flower buds with epicalyx; epicalyx horizontal or pendulous; lanceolate, 1.5–1.6 × 0.6–0.7 cm, densely pubescent. Epicalyx present after flowers at anthesis, 1.3–1.5 × 0.2–0.4 cm; epicalyx lobe linear, margin pinnately partite, densely fringed, densely woolly stellate pilose. Calyx and corolla 5 - merous. Sepals 5, valvate, linear – lanceolate, 2.0–2.9 × 0.47–0.53 cm; abaxially stellate hairy, adaxially villous. Petals 5, yellow to orange, oblong-rectangle; petals are turned backwards between the sepals; 1.3–1.5 × 0.6–0.7 cm, broader than sepals; above part glabrous; apex entire to emarginate; narrowed towards the base, claw broad, thick densely pubescent, deflexed between the sepals. Stamens many, connate into cylindrical tube; staminal tube covering the ovary and style, 1.1–1.3 cm long; anthers linear-oblong to rectangular, 0.21–0.31 × 0.04 cm, 2 - celled, cells parallel. Ovary superior, ovate, 0.07–0.08 × 0.05–0.06 cm, pubescent; style linear, simple, 2.0– 2.2 cm long, style significantly exceeds staminal tube length; stigma 5–7 - lobed, lobes needle-like, horizontal to down-curved. Capsules ovate-elliptic, woody, 2.0–2.5 × 1.3–1.8 cm, longitudinally grooved, fruit apex round; fruit stalk 3.5–3.7 cm long; densely hairy.

Etymology.

The specific epithet refers to the type locality, Bac Giang Province in Vietnam.

Distribution and ecology.

E. bacgiangensis is found only in Vietnam, Bac Giang Province, Son Dong District, Huu San Commune, where it grows in well-lit places in shrubland and dry soil of secondary forest, in association with Acacia mangium Willd. , Bidens pilosa L. , Cayratia trifolia (L.) Mabb. & J. Wen , Chromolaena odorata (L.) R. M. King & H. Rob . and Stachytarpheta jamaicensis (L.) Vahl . Flowering and fruiting specimens were collected in July 2015.

Conservation status.

Data Deficient (DD) ( IUCN 2025). Eriolaena bacgiangensis is known only from the type locality. A comprehensive botanical survey of the Eriolaena has not been carried out to date. Potential threats from habitat fragmentation for road construction and land-use change for Acacia spp. plantations, therefore, require urgent and appropriate plans for ex situ species conservation.

Figures

Figure 1. Eriolaena bacgiangensis T. H. Bui A habit B flowering, fruiting branch C leaves D cordate base E dentate margin F flower bud and flower G epicalyx lobes H – J flower K flower from below L staminal tube, style, stigma M, N fruit (Photos by T. B. Tran).

Figure 2. Eriolaena bacgiangensis T. H. Bui A flowering, fruiting branch B pubescent branch C pubescent leave D – F stellate hairs on leaves G fruit (Drawn by Le Kim Chi).

Figure 3. Eriolaena bacgiangensis T. H. Bui A flower bud B, C bloom flower D epicalyx lobes E, G flower F flower from below H staminal tube, style, stigma I stamens J fruit (Drawn by Le Kim Chi).