The new species belongs to the section Appendiculatae as the leaf lamina has basal adaxial glands, disc-like glands unevenly scattered within the arches of the marginal veins throughout the abaxial surface of the lamina (Fig. 2B), papillate stigmas, and pubescent septae and column in the ovary (Fig. 2E) (Schot 2004), but is distinguished from previously known species by its tetragonal ovary of the pistillate flower and the fruit.
The Neighbor-joining tree based on rbcL and matK supports the separation of each morphologically defined section and the monophyly of sect. Appendiculatae, sect. Benthamianae and sect. Sundanenses with 98 %, 76 % and 85 % bootstrap probability, respectively. The new species was placed in sect. Appendiculatae and clearly separated from other species of this section with a sister relationship to the clade including A. ficifolia, A. odctandra var. octandra, A. planchoniana and A. villosa.
Thus, the species is morphologically distinct from known taxa and the phylogeny supports the separation from related species. Here, we define the new species Aporosa tetragona Tagane & V. S. Dang.
Aporosa tetragona Tagane & V. S. Dang, sp. nov.
Aporosa tetragona is distinct from all other Aporosa species by having a tetragonal ovary and fruit. The leaves are similar to Aporosa acuminata Thwaites, but differing in not only fruit shape but also wider leaves (vs. 2–4 cm wide), larger pistillate flowers (vs. 2–3.5 mm long), and glabrous fruits (vs. sparsely puberulous).
VIETNAM. Khanh Hoa Province, Mt. Hon Ba, edge of evergreen forest near stream, 12°06'30.60"N, 108°59'15.70"E, alt. 393 m, 22 November 2014, with female fl. and fr., Toyama H., Tagane S., Dang. V. S., Nagamasu H., Naiki A., Tran H., Yang C. J. V1976 (holotype KYO!, isotypes BKF!, FU!, K, NTU!, P, VNM!, the herbarium of Hon Ba Nature Reserve!).
Aporosa tetragona sp. nov.
A Leafy branch B Fruits and portion of abaxial surface of young leave C Apical bud and pulvinate petiole at both base and apex D Pistillate inflorescence E Fruits F, G Transverse section of fruits H Seeds taken from fruits. Materials: Toyama et al. V1976.
Small tree, 3 m tall. Twigs glabrous, young branchlets green in vivo, dull yellowish green to pale yellow in sicco, old branchlets light grayish brown. Stipules caducous, not seen. Leaves: petiole 0.8–1.7 cm long, sunken above, rounded below, pulvini distinct, glabrous; blade ovate to elliptic, (6.8–)9–16.5 × 3.9–7.0 cm, length/width ratio 2.0–2.9, chartaceous to subcoriaceus, completely glabrous, dull yellowish green to dull pale yellow above and beneath in sicco, base cuneate to rounded, or shallowly subcordate, basal glands present, margin entire, foliar glands abaxially scattered mostly within the arches of the marginal veins, apex acuminate, acumen up to 2.3 mm long; midrib prominent on both surfaces, or rarely sunken only on the upper surface, secondary veins 10–14 pairs, raised on the lower surface, tertiary veins reticulate, visible on both surfaces of young leaves in sicco, inconspicuous on lower surface of old leaves. Staminate inflorescences not seen. Pistillate inflorescences in axils of leaves near the top of branchlets, solitary, flowers up to 7, rachis 2–5 mm long, densely pubescent; bracts broadly triangular, ca. 1 × 1.1 mm, margin ciliate, very sparsely pubescent outside, glabrous inside. Pistillate flowers (6–)8–10 mm long, (1.8–)2.5–3 mm in diam., sessile, yellowish in vivo, reddish brown in sicco; sepals 4, triangular, 0.8–1.1 × 1.1 mm, glabrous to very sparsely hairy outside, glabrous inside except near base, margin ciliate; ovary obclavate, 5–9 mm long, tetragonal, 2-locular, glabrous outside; ovules 2 per locule; stigmas slightly raised, elongated, ascending from the top of the ovary, stigma bilobed, lobes ca. 0.6–1 mm long, each stigma lobe apically deeply bifid, papillate and hairless above, smooth and very sparsely hairy beneath, style remnant present. Fruits tetragonal ellipsoid with sharp ridges, 21–25 × 7–9 mm, stiped, beaked, fleshy, reddish in vivo, pinkish orange to reddish brown in sicco, glabrous; septae and column pubescent with hairs of 0.4–0.6 mm long. Seeds 2 or 3, ellipsoid, flattened, ca. 9.0 × 5.0 × 3.5–4 mm, covered by fleshy, yellow aril in vivo, yellowish brown in sicco.
Aporosa tetragona sp. nov.
A Fruiting branch B Schematic of the placement of the disc-like glands on the lower side of the leaf C Apex of branch D Pistillate inflorescence E Longitudinal section of fruits. Materials: A–C, E from Toyama et al. V1976 (KYO), D from Toyama et al. V829 (FU).
Other specimen examined
Vietnam. Khanh Hoa Province, Mt. Hon Ba, in evergreen forest near river, 12°06'33.41"N, 108°59'24.89"E, alt. 367 m, 19 Feb. 2014, with female fl., Toyama et al. V829 (FU!, VNM!, the herbarium of Hon Ba Nature Reserve!).
Flowering specimens were collected in July and November; fruiting in November.
Distribution and habitat
This species is currently known only from Hon Ba Nature Reserve, Khanh Hoa Province, South Vietnam. The small populations were found at the edge of humid broad-leaved evergreen forest close to a stream, altitude 200–400 m.
The specific epithet tetragona reflects the quadrangular shape of the ovaries in the pistillate flowers and fruits.
GenBank accession No
Toyama et al. V1976: LC050338 (rbcL), LC050339 (matK).
The species is known only from the type locality in Mt. Hon Ba at 200–400 m altitude. It is suggested that Aporosa tetragona should be placed under the IUCN category ‘Critically Endangered’ (CR) (IUCN 2012) because of its limited distribution with an area of occupancy estimated to be less than 10 km2 (criterion B2 a) and a small number of individuals estimated to be less than 250. Recent botanical inventories carried out in this narrow area along stream discovered several new species, including Dillenia tetrapetala Joongku Lee, T. B. Tran & R. K. Choudhary (Choudhary et al. 2012), Goniothalamus flagellistylus Tagane & V. S. Dang (Tagane et al. 2015) and Vanilla atropogon Schuit., Aver. & Rybková (Schuiteman et al. 2012), all of which are rare and endemic to Mt. Hon Ba. Therefore further collection efforts around this area are necessary to accurately understand the flora there and to update the conservation status of the species.