Metapetrocosmea alba X. R. Zheng, P. S Zou & S. P. Dai 2023, sp. nov.

Metapetrocosmea alba X. R. Zheng, P. S Zou & S. P. Dai, sp. nov. (Figs. 1 & 2).

Type:— VIETNAM. Thua Thien Hue Province: Hue City, Bach Ma National Park, the lowland montane, ca. 100 m a.s.l., specimens were collected from wild plants introduced and cultivated at the nursery of the Guangzhou Institute of Forestry and Landscape Architecture, 16 Sep. 2022, Xi-Rong Zheng ZXR216 (holotype: IBSC!; isotype: IBK!, VNMN!).

Diagnosis:— The new species is most similar to M. poilanei in the distinct stem and similar calyx, but radically differs by its longer (12–14 mm vs. 10 mm) and white (vs. light violet) obliquely funnelform (vs. obliquely campanulate) corolla and three (vs. two) staminodes. And it is easy to distinguish the new species from M. cycnostyla by its distinct (vs. very short) stem, leaf blade shape (ovate or broadly ovate vs. elliptic) and size (4–8 × 3–5 cm vs. 2–3 × 1.5–2 cm).

Description:— Herb, perennial, stem erect, 10–15 cm tall, sparsely villous. Leaves alternate; petiole 2–8 cm long, sparsely villous; blade carnose, adaxially sparsely glandular villous, abaxially glabrous, ovate or broadly ovate, 4– 8 × 3–5 cm, apex subacute, base lightly peltate, round or cordate, margin shallowly obtuse-dentate or shallowly undulateserrate, slightly curved, densely villous; venation penninerved, lateral veins 5–6 on each side of mid-rib. Inflorescence compound cymes, axillary, fasciculate; peduncle 10–18 cm long, densely glandular villous; bracts 2, ovate, 5–9 × ca. 5 mm, abaxially glandular villous, adaxially glabrous; bracteoles 2, ovate, ca. 5 × 3 mm, abaxially glandular villous, adaxially glabrous; pedicel 8–10 mm long, densely glandular villous. Calyx 5-parted to the base, with lobes lanceolate, ca. 5 × 1.5 mm, margin entire, outside densely glandular villous, inside sparsely glandular villous. Corolla obliquely funnelform, zygomorphic, white, 12–14 mm long, ca. 3 mm wide at the throat, outside densely pubescent, inside glabrous; tube ca. 12 mm long; limb distinctly 2-lipped; adaxial lip 2-lobed, lobes semi-circular, ca. 3 × 2 mm, abaxial lip 3-lobed, lobes semi-circular, ca. 4 × 3 mm. Fertile stamens 2, adnate to the base of corolla tube, coherent in pair at the belly of anther, filaments ca. 4 mm long; staminode 3, adnate to the base of corolla tube, ca. 1.5 mm long. Disc ring-like, ca. 0.8 mm high, glabrous. Pistil ca. 10 mm long; ovary linear, densely glandular pubescent, ca. 4 mm long; style linear, ca. 6 mm long; stigma obtrapeziform, broad, flat and emarginate. Capsule obliquely narrowly oblong, ca. 11 mm long, 1.5–2 mm in diameter, slightly curved, dehiscing loculicidally to base, splitting along one suture, straight, not twisted.

Distribution and habitat:— This new species only occurs in a lowland montane area, Bach Ma National Park, Hue City, Thua Thien Hue Province, Vietnam. The plants grow on the moist rock by the stream, in association with a species of Begonia L. and several fern species.

Provisionally conservation status:— This species has been only observed from the type locality and the accurate distribution range has not been ascertained. More information of its distribution and number of individuals requires further field investigation for accurate evaluation. This species is therefore preliminarily assigned as “Data Deficient” [DD] following IUCN Red List Categories and Criteria (IUCN, 2012).

Etymology:— The species epithet refers to the white colour of calyx and corolla.

Notes:— In our nursery, this species blooms almost all year round and its magnificent white flower clusters make it an excellent ornamental plant.