Helicteres binhthuanensis V.S.Dang, 2020

Dang, Van-Son, Dang, Minh-Quan & Hoang, Nghia-Son, 2020, Helicteres binhthuanensis V. S. Dang (Malvaceae, Helicteroideae), a new species from southern Vietnam, PhytoKeys 166, pp. 87-95 : 87

Helicteres binhthuanensis V.S.Dang sp. nov. Figures 2 , 3

Diagnosis.

Similar to Helicteres angustifolia L. (Figure 4 ) in its shrubby habit (to 2 m tall) and axillary inflorescences but distinguished by the size of its leaf blades (10-13 × 0.8-1.2 cm vs. 3-15 × 1-4 cm), larger petals (12-16 mm long vs. 5-10 mm long), longer androgynophores (10-15 mm long vs. 3-7.5 mm long), and stamen number (10 vs. 15). Also similar to H. sphaerotheca Cowie, but differs from the latter by having larger leaf blades (10-13 × 0.8-1.2 cm vs. 1.5-3.5 × 0.2-0.7 cm), longer stipules (3-4 mm long vs. 1-2 mm long) and bracts (1-2 mm long vs. 1 mm long), larger calyx (tube 6-8 mm long, lobes 4-5 mm long vs. tube 3.5-4.5 mm long, lobes ca. 0.5 mm long) and petals (12-16 mm long vs. 7-9.5 mm long), and fruit shape (ovoid to ellipsoid vs. globular).

Type.

Vietnam. Binh Thuan Province, Ham Thuan Bac District, 40 km north of Phan Thiet City, in secondary forests, 11°07 ’02.30” N, 108°14 ’92.07” E, 80 m alt., 20 July 2019, Van-Son Dang & Nghia-Son Hoang, Dang 386 (holotype: VNM; isotypes: HN, VNM, VNMN).

Description.

Shrubs, 1-2 m tall; branches slender, 2-3 mm in diam., densely yellow-brown stellate puberulent. Leaves alternate, blades narrowly lanceolate to narrowly oblanceolate, 10-13 × 0.8-1.2 cm, coriaceous, yellowish brown when dry, adaxially sparsely puberulent, abaxially densely yellow-brown puberulent, apex acute or acuminate, base rounded, symmetric, margin entire; midrib flat or slightly depressed adaxially, distinct and prominent abaxially; secondary veins 3-7 pairs, obscure adaxially, prominent abaxially; petioles 5-8 mm long, densely yellow-brown puberulent. Stipules persistent, 3-4 mm long, filiform or linear, densely pubescent. Inflorescences axillary or terminal, cymose, 8-14 mm long, 2-5-flowered; bracts 1-2 mm long; pedicels 1-5 mm long. Flowers with short pedicel; calyx tubular to campanulate, 10-13 mm long, whitish green, densely villous to hirsute, calyx tube 6-8 mm long, calyx lobes 5, unequal, lanceolate to triangular, 4-5 mm long, tips acute; petals 5, unequal in length, 12-16 mm long, whitish pink or purplish, darker at base of limb, reflexed at anthesis, limb cuneate, densely hirsute, callused near base, apex truncate, lower 3 petals slightly longer than upper pair, claw with 2 or 1 auriculate appendices, upper pair with 2 prominent appendages on the claw; androgynophore 10-15 mm long, straight, villous at base; stamens 10, shortly connate at base; staminodes 5, broadly lanceolate; filaments coalescent, surrounding ovary; anthers transverse, oblong; ovary ovoid or globose, 5-locular, densely villous; style 1.3-1.5 mm long; stigma 5-toothed, terete. Fruit a capsule, ovoid to ellipsoid, 1.5-2 × 0.8-1 cm, with 5 longitudinal lobes, densely villous, apex short-beaked, black when mature; seeds many, small, 2.5-4 × 1.5-2 mm, irregularly rugose, dark brown, angled when dry.

Other specimen examined.

Vietnam. Binh Thuan Province, Ham Thuan Bac District, 40 km north of Phan Thiet City, in secondary forests, 11°07 ’02.33” N, 108°14 ’92.27” E, 86 m elevation, 21 July 2019, Van-Son Dang & Nghia-Son Hoang, Dang 383 (VNM).

Phenology.

Flowering and fruiting specimens were collected in July.

Distribution and habitat.

Helicteres binhthuanensis is known only from Ham Thuan Bac District, Binh Thuan Province, southern Vietnam. It grows along roadsides and edges of secondary forests at ca. 80-95 m elevation.

Etymology.

The species epithet is derived from the name of the province (Binh Thuan) where the species was discovered.

Vernacular names.

Tổ kén bình thuận, An xoa bình thuận.

Preliminary conservation assessment.

Helicteres binhthuanensis was collected from a small population in a habitat that was logged and disturbed. Therefore, we suggest its placement in the Data Deficient (DD) category based on the IUCN Red List Categories ( IUCN 2019).

Notes.

Morphologically, Helicteres binhthuanensis is most similar to H. angustifolia , which is a common species in mainland southeast Asia, and H. sphaerotheca , which is endemic to the Northern Territory of Australia, between the Mary River and the South Alligator River. It differs from those species in several characters that are summarised in Table 1 .

Figures

Figure 2. Habitat and habit of Helicteres binhthuanensis A habitat B habit. Photos by Van-Son Dang.

Figure 3. Helicteres binhthuanensis A, B flowering and fruiting branches C close-up of young leaves and stipules D abaxial leaf surface E-G close-up of axillary inflorescence and flowers H-J close-up of fruits K Seeds. Photos by Van-Son Dang.

Figure 4. Helicteres angustifolia A flowering branches B abaxial leaf surfaces C close-up of axillary inflorescence and flowers D, E close-up of fruits. Photos by Van-Son Dang.