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Research Article
Helicteres binhthuanensis V.S.Dang (Malvaceae, Helicteroideae), a new species from southern Vietnam
expand article infoVan-Son Dang‡§, Minh-Quan Dang|, Nghia-Son Hoang‡§
‡ Vietnam Academy of Science and Technology, Ho Chi Minh, Vietnam
§ Graduate University of Science and Technology, Ha Noi, Vietnam
| Can Tho University, Can Tho, Vietnam

Corresponding author: Van-Son Dang ( dvsonitb@gmail.com )

Academic editor: Laurence J. Dorr
© 2020 Van-Son Dang, Minh-Quan Dang, Nghia-Son Hoang.
This is an open access article distributed under the terms of the CC0 Public Domain Dedication.
Citation: Dang V-S, Dang M-Q, Hoang N-S (2020) Helicteres binhthuanensis V.S.Dang (Malvaceae, Helicteroideae), a new species from southern Vietnam. PhytoKeys 166: 87-95. https://doi.org/10.3897/phytokeys.166.57647
Open Access

Abstract

Helicteres binhthuanensis V.S.Dang, sp. nov. from Ham Thuan Bac District, Binh Thuan Province, Vietnam is described and illustrated. It is morphologically similar to H. angustifolia, which is a common species in mainland southeast Asia, and H. sphaerotheca, which is endemic to the Northern Territory, Australia, but differs from both by several salient characters such as leaf and calyx size, androgynophore length, petal color, and fruit shape. Photographs, a vernacular name, a preliminary conservation assessment, and a table of morphological characters comparing this new species to two closely related species also are provided.

Keywords

Helicteres, Helicteroideae, Malvaceae, Vietnam

Introduction

Helicteres L. comprises about 60 species in the tropics of Asia and America (Cowie 2011). The genus was included in a broadly-defined Sterculiaceae by Cronquist (1981), but more recently is included in Malvaceae sensu lato based on morphological and molecular evidence (Mabberley 2008; APG IV 2016). The genus is characterized by the stamens and pistil forming an androgynophore, sepals united, petals unguiculate, capsules cylindrical, fusiform or ovoid, spiral or rarely straight, pubescent, and seeds wingless due to parenchymal expansion (Cristóbal 2001; Chantaranothai and Poompo 2019). Currently, nine species and one variety of the genus have been recorded in Vietnam: H. angustifolia L., H. angustifolia var. glaucoides Pierre, H. daknongensis V.S.Dang & D.T.Bui, H. elongata Wall. ex Mast., H. hirsuta Lour., H. isora L., H. lanata (Teijsm. & Binn.) Kurz, H. lanceolata DC., H. poilanei Tardieu, and H. viscida Blume (Hoang et al. 2020).

During fieldwork in July 2019, we collected several specimens of Helicteres in Ham Thuan Bac District, Binh Thuan Province, southern Vietnam (Figure 1). After morphological study and reviewing the relevant literature from Vietnam and neighboring countries (Tardieu-Blot 1945; Pham 1999; Cristóbal 2001; Phengklai 2001; Nguyen 2003; Tang et al. 2007; Cowie 2011), as well as comparing our material with specimens in several Vietnamese herbaria (HN, VNM, and VNMN) and images available via JSTOR Global Plants, K, and P (all acronyms follow Thiers 2020, continuously updated), we confirm that this material is distinct from previously known taxa. Here, we describe it as a new species, H. binhthuanensis V.S.Dang.

Figure 1. 

Type locality of Helicteres binhthuanensis.

Materials and methods

Our description of the new species is based on observations from living and dried specimens; measurements were made using a ruler accurate to 0.5 mm. Voucher specimens were deposited in HN, VNM, and VNMN. The photographs were taken with a Canon 1000D camera fitted with an EF 100 mm f/2.8 Macro USM lens. The conservation status of the new species was assessed according to the International Union for Conservation of Nature (IUCN 2019).

Taxonomic treatment

Helicteres binhthuanensis V.S.Dang, sp. nov.

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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).

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.

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.

Table 1.
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Comparison of Helicteres binhthuanensis with its morphologically closest allies (modified from Pham 1999; Phengklai 2001; Tang et al. 2007; Cowie 2011).

Character H. binhthuanensis H. angustifolia H. sphaerotheca
Branch indumentum densely yellow-brown stellate puberulent gray greenish puberulent sparsely stellate hairy, hairs sessile
Petiole length 5–8 mm long 3–15 mm long 0.5–1 mm long
Leaf blade size 10–13 × 0.8–1.2 cm 3–15 × 1–4 cm 1.5–3.5 × 0.2–0.7 cm
Stipule length 3–4 mm long 3.5–6 mm long 1–2 mm long
Bract length 1–2 mm long 1.5–2 mm long ca. 1 mm long
Calyx tube length 6–8 mm long ca. 6 mm long 3.5–4.5 mm long
Calyx lobe length 4–5 mm long 3–4 mm long ca. 0.5 mm long
Petal color at anthesis whitish pink or purplish bluish or pink mauve-pink
Petal length 12–16 mm long 5–10 mm long 7–9.5 mm long
Androgynophore length 10–15 mm long 3–7.5 mm long 4.5–5 mm long
Number of stamens 10 15 10
Number of staminodes 5 O 5
Fruit shape ovoid to ellipsoid ovate to oblong globular
Seed length 2.5–4 mm long 2–3.5 mm long ca. 2.5 mm long

Acknowledgements

We thank the curators and staff of the herbaria at the HN, VNM, and VNMN for their help in accessing specimens. This work was supported by the Institute of Tropical Biology, Vietnam Academy of Science and Technology, Vietnam.

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