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Loxostigma puhoatense (Gesneriaceae), a new species from North Central Vietnam
expand article infoNgọc-Sâm §, Danh-Hùng Nguyễn§, Thị-Hương |, Minh-Hợi Trần, Ngọc-Đài Đỗ§#, Bá-Vương Trương, Stephen Maciejewski¤
‡ Institute of Tropical Biology, Vietnam Academy of Science and Technology, Ho Chi Minh, Vietnam
§ Graduate University of Science and Technology, Hanoi, Vietnam
| Vinh University, Vinh, Vietnam
¶ Institute of Ecology and Biological Resources, Hanoi, Vietnam
# Nghe An College of Economics, Vinh, Vietnam
¤ The Gesneriad Society, Seattle, United States of America
Open Access

Abstract

Loxostigma puhoatense N.D. Do et al., sp. nov., a new species of Gesneriaceae, is described and illustrated from Pu Hoat Nature Reserve, Nghe An Province, Vietnam. This species is morphologically similar to L. dongxingensis and L. damingshanensis in the plant habit, indumentum system of vegetative and reproductive characters, shape of leaf blades, calyx, pistil but differs from the latter two by the abaxially reddish-purple leaf blade with pubescent along veins, lateral veins 11–19, shorter white to pale yellowish-white corolla (3.7–3.8 cm long) with purple-spotted and glabrous inside, longer abaxial stamens in 2–2.1 cm, shorter and densely glandular-puberulent ovary in 1–1.2 cm, and sparsely glandular-puberulent style. Data on distribution, ecology, phenology, and vernacular of the new species are provided.

Keywords

Briggsia, Didymocarpus, Gesneriaceae, Loxostigma, taxonomy, Vietnam

Introduction

The genus Loxostigma C.B. Clarke is in the family Gesneriaceae, with at least 11 species recognized including one species from Didymocarpus Wallich and three species of the former Briggsia Craib (Möller et al. 2014) based on molecular and morphological evidences (Pan 1988; Wu et al. 2012; Möller et al.2011; Möller et al. 2014). It is distributed mainly in Southern and Southeastern Asia, and most of the species have restricted distributions in southwestern China (Wang 1983; Wei et al. 2010; Möller et al. 2014, 2016). There are four currently known species of the genus in Vietnam, namely Loxostigma dongxingensis (Chun ex K.Y.Pan) Mich. Möller & Y.M.Shui, L. fimbrisepalum K.Y.Pan, L. glabrifolium D.Fang & K.Y.Pan and L. griffithii (Wight) C.B. Clarke (Pham 2000; Vu 2005; Do and Vu 2011; Möller et al. 2014; Do et al. 2016).

During our recent botanical surveys of Pu Hoat Nature Reserve (NR), Nghe An, Vietnam, an unknown species of Loxostigma with the seeds having 1-hairlike appendage at each end was collected by the authors in 2018–2019. We conducted a critical examination of the specimens, and made a comparison with type material and protologues of presumed closely related species in Vietnam and neighboring countries (e.g. Wang 1983; Wang and Pan 1982; Pan 1988; Wang et al. 1998; Grierson and Long 2001; Li and Wang 2004; Wei et al. 2010; Sinha and Datta 2016). We discovered that these specimens were different from the other known Loxostigma species and presented the unknown taxon which shows similarities with L. dongxingensis and L. damingshanensis (L.Wu & B.Pan) Mich.Möller & H.Atkins in the same plant habit, indumentum of stem and shape of flower. However, it shows significant differences in its vegetative and floral structures (see Table 1) and is described here as a new species to science.

Material and methods

All measurements and description of the new species are based on living flowering material and herbarium specimens collected from the type locality, supplemented with type material from the following herbaria: HITBC, HN, IBK, IBSC, K, KUN, P, PE, VNM and VNMN (herbarium codes follow Thiers (2018)) as well as digitized specimen images of Loxostigma species available on the web from Muséum National d’Histoire Naturelle (https://science.mnhn.fr/), Chinese Virtual Herbarium (http://www.cvh.ac.cn/) and Jstor Global Plant (https://plants.jstor.org/). All morphological characters were studied under dissecting microscopes and are described using the terminology presented by Wang et al. (1998), Wei et al. (2010) and Beentje (2016).

Taxonomic treatment

Loxostigma puhoatense N.D. Do, N.S. Ly, D.H. Nguyen & T.H. Le, sp. nov.

Figs 1, 2

Diagnosis

This species is most similar to L. dongxingensis and L. damingshanensis in the plant habit, indumentum system of stem, leaves, shape of leaf blades, calyx and pistil but differs from the latter two in the leaf blade with abaxially reddish-purple and number of lateral veins, longer peduncle, shorter white to pale yellowish-white corolla with purple-spotted inside, longer abaxially stamens that are lower adnate above corolla tube base, shorter and glandular-puberulent ovary, and sparsely glandular-puberulent style.

Figure 1. 

Loxostigma puhoatense (from the holotype). A mature plant with flowers B a part of stem C inflorescence D dorsal view of flower E opened flower showing stamens F gynoeciums G detail of stigma (from dry specimen) H infructescence I seeds. Drawn by Ba-Vuong Truong from Do Ngoc Dai, Nguyen Danh Hung, Le Thi Huong, DHH 1021.

Type

Vietnam. Nghe An Province: Tien Phong Commune, Na Chang Village, Pu Hoat NP, 19°46'06"N, 109°55'08"E, atl. 781 m, 04 October 2018, Do Ngoc Dai, Nguyen Danh Hung, Le Thi Huong, DHH 1021 (holotype: VNM, isotype: P).

Description

Epiphyte, evergreen, perennial herbs with rhizomes. Rhizome internodes up to 20 cm long, 3.5–4 mm in diam. Stem simple, borne from a node of the rhizome, shallow angular at the middle internodes, terete toward both ends, 28.5–55 cm long, 3.5–7 mm in diam., pale green, somewhat pubescent. Leaves opposite, spread along stem, unequal in a pair; petiole cylindrical, adaxially sunken, greenish to purplish, abaxially rounded and greenish, 1–3.3 cm long, 3–6 mm in diam., pubescent; leaf blade broadly elliptic to elliptic-ovate, chartaceous when dried, 4.2–25.5 × 3–15.5 cm [11.3–25.5 × 8.9–15.5 cm in larger leaves, 4.2–9.3 × 3–6.2 cm in smaller leave], adaxially light green, abaxially reddish purple, sparsely pubescent on both surface, pubescent on the midrib and lateral veins of the abaxial surface, lateral veins 11–19 pairs, base usually oblique, subcordate, margin serrate to indistinctly denticulate, apex acuminate. Cymes axillary, subterminal, 2–3-branched, 3–25-flowered; peduncle 9.2–17.5 cm long, 2–3 mm in diam., pale greenish, densely pubescent and glandular-pubescent. Bracts ovate to oblong-ovate, pale greenish-white tinted, 5–8.5 × 2.8–3.5 mm, adaxially glabrous, abaxially densely pubescent and glandular-pubescent, margin somewhat denticulate. Pedicel 1.1–1.4 cm long, ca. 1.5 mm in diam., greenish-white, densely pubescent and glandular-pubescent. Calyx 5-sect from the base, segments equal, whitish, narrowly ovate, 6–7 × 2–2.5 mm, adaxially glabrous, abaxially densely pubescent and glandular-pubescent, margin entire, apex acute. Corolla somewhat campanulate, white to pale yellowish-white, gibbous abaxially, with purple spots inside, 3.7–3.8 cm long, outside densely glandular-pubescent, inside glabrous; corolla tube 2.7–2.9 × 1.4–1.6 cm; corolla limb distinctly 2-lipped, adaxial lip 5–6 mm long, 2-lobed, lobes semi-orbicular, 5–5.5 × 7–7.5 mm, deflexed, apex rounded; abaxial lip3-lobed, 10–11 mm long, lobes semi-orbicular, 4–5.5 × 4–5 mm, deflexed, apex rounded. Stamens 4, adaxial stamens adnate to 7–8 mm above corolla tube base, 15–16 mm long, abaxial ones adnate to 6–7 mm above corolla tube base, 20–21 mm long; filaments linear, white, glabrous, slightly curved; anthers sub-globose, theca coherent apically in pairs, pale cream; staminode one, adnate to 7–8 mm above corolla tube base, ca. 2 mm long. Disc ring-like, subentire, ca. 2.5mm high. Pistil 2.2–2.4 cm long; ovary oblong, greenish, 10–12 × 1.8–2 mm, densely glandular-puberulent; style linear, pale greenish, 9–10 × ca. 1 mm, sparsely glandular-puberulent; stigma 2, equal, 2-lipped, undivided. Capsule 6–6.5 cm long, 2–3mm in diam., oblong-linear, straight, not twisted, glabrous, blackish-brown, dehiscing loculicidally to base, valves 2. Seeds linear, 2–2.5 mm long, brown, with appendages on both ends of the seeds; appendages 2.5–3 mm long.

Distribution and habitat

Loxostigma puhoatense is currently known from a single population with eight mature plants, in tropical evergreen broad-leaf forests, Pu Hoat Nature Reserve, Nghe An Province. More data is needed to determine conservation status. It is an epiphytic plant (Fig. 2A), growing on the surface of Ficus sp. (Moracaeae), and is associated with fern (e.g. Asplenium nidus L. (Aspleniaceae), epiphytic herbs (e.g. Aeschynanthus acuminatus Wall. ex A. DC. (Gesneriaceae), Pothos chinensis (Raf.) Merr. (Araceae) and is dominated by Beilschmiedia ferruginea H.Liu, Cinnamomum polyadelphum (Lour.) Kosterm., C. tamala (Buch.-Ham.) T.Nees & Eberm., Lithocarpus balansae (Drake) A. Camus, Syzygium grande (Wight) Walp., S. odoratum (Lour.) DC., Gordonia axillaris (Roxb. ex Ker Gawl.) Endl…

Figure 2. 

Loxostigma puhoatense. A plant in natural habitat B apical part of flowering plant showing inflorescences (with flowers and young fruits) and leaves C inflorescence D abaxial leaf E adaxial leaf F flower (from below) G flower (top view) H flower (front view) I longitudinal section with upper lip removed J stamens with gynoecium and calyxes K dried fruits. Photos by Ngoc-Dai Do, plate by Ngoc-Sam Ly.

Phenology

Flowering in October–December and fruiting November–February.

Etymology

The specific epithet “puhoatense” is derived from the type locality.

Other specimens examined (Paratypes)

Vietnam. Nghe An Province: Pu Hoat NP, 24 February 2019, 19°46'06"N, 109°55'07"E, Do Ngoc Dai, Nguyen Danh Hung, Nguyen Thi Huong, DHH 1162 (VNM).

Vernacular name

Vietnamese language: Xuyến thư pù hoạt

Taxonomic notes

Loxostigma puhoatense is morphologically similar to L. dongxingensis and L. damingshanensis in the plant habit, somewhat pubescent stem, elliptic to ovate leaf lades, narrowly ovate calyx with margin entire, the same shape of flower. However, the new species differs from both of them in the abaxially reddish-purple leaf blade with pubescent along veins (vs green, villous of L. dongxingensis and pilose of L. damingshanensis), lateral veins 11–19 pairs (vs. 6–10 pairs and 5–10 pairs of the latter two, respectively), shorter white to pale yellowish-white corolla (3.7–3.8 cm long) with purple-spotted and glabrous inside (vs. 4–5 cm long, yellow, inside spotted or not and sparsely pubescent only on lobes of adaxial lip of L. dongxingensis, and 4.8–6 cm long, yellow, inside purple stripes and sparsely pubescent only on lobes of abaxial lip, of L. damingshanensis), longer abaxial stamens in 2–2.1 cm long (vs. ca. 18 cm and ca. 14 cm in the latter two, respectively), shorter and densely glandular-puberulent ovary in 1–1.2 cm long (vs. ca. 2 cm, glabrous of L. dongxingensis and ca.1.8 cm, densely glandular-pubescent of L. damingshanensis), and sparsely glandular-puberulent style (vs. glandular-pubescent of L. dongxingensis and L. damingshanensis). The staminode of L. puhoatense is ca. 2 mm long (vs. ca. 1 mm of L. dongxingensis and ca. 1.5 mm of L. damingshanensis) and adnate above corolla tube base in 0.7–0.8 mm long (vs. ca. 1.3 cm of L. dongxingensis and ca. 1.8 cm of L. damingshanensis). Furthermore, the densely pilose petiole of L. dongxingensis is distinguished with the somewhat pubescent petiole of L. puhoatense and L. damingshanensis. The unbranched cyme and inconspicuous or absent of bract of L. damingshanensis are distinct with the branched cyme and 2- somewhat ovate bracts of the remained two. A detailed morphological comparison between L. puhoatense, L. dongxingensis, and L. damingshanensis is provided in Table 1.

Morphological comparison of Loxostigma puhoatense, L. dongxingensis and L. damingshanensis.

Characters L. puhoatense L. dongxingensis L. damingshanensis
Stem somewhat pubescent densely pubescent sparsely pubescent
Leaf blade broadly elliptic to elliptic-ovate, abaxially reddish-purple, sparsely pubescent on both surfaces, pubescent along veins, lateral vein 11–19 pairs elliptic to ovate or obovate, abaxially green, adaxially appressed puberulent to pubescent, abaxially pubescent, villous along veins, lateral vein 6–10 pairs elliptic-ovate, abaxially green, sparsely pubescent on both surfaces, pilose along veins, lateral veins 5–10 pairs
Petiole pubescent densely pilose sparsely pubescent
Cyme branched branched unbranched
Peduncle 9.2–17.5 cm long, densely pubescent and glandular-pubescent 4–10 cm long, pubescent 4–8 cm long, sparsely glandular-pubescent
Bract ovate to oblong-ovate, densely pubescent and glandular-pubescent, margin somewhat denticulate narrowly ovate to narrowly oblong, pubescent, margin entire inconspicuous or absent
Pedicel densely glandular-pubescent pubescent sparsely glandular-pubescent
Calyx outside densely glandular-pubescent outside pubescent to villous outside densely glandular-pubescent
Corolla white to pale yellowish-white with purple-spotted inside, 3.7–3.8 cm long, outside densely glandular pubescent, inside glabrous yellow, inside spotted or not, 4–5 cm long, outside sparsely pubescent, inside sparsely pubescent only on lobes of adaxial lip yellow, inside with purple stripes, 4.8–6 cm long, outside sparsely glandular-pubescent, inside sparsely pubescent only on lobes of abaxial lip
Staminode ca. 2 mm long, adnate 7–8 mm above corolla tube base ca. 1 mm long, adnate to ca. 13 mm above corolla tube base ca. 1.5 mm long, adnate to ca. 18 mm above corolla tube base
Abaxial stamens 2–2.1 cm long ca. 1.8 cm long ca. 1.4 cm long
Ovary 1–1.2 cm long, densely glandular-puberulent ca. 2 cm long, glabrous ca. 1.8 cm long, densely glandular-pubescent
Style sparsely glandular-puberulent glandular pubescent glandular-pubescent

A key to known species of Loxostigma occurring in Vietnam

1 Calyx lobes narrowly ovate. Peduncle somewhat pubescent. Stem usually less than 60 cm tall 2
Calyx lobes ovate to broadly ovate or oblanceolate. Peduncle somewhat puberulent. Stem usually ≥ 60 cm tall 4
2 Stem pubescent. Leaf blades somewhat hairs on both surfaces, abaxially pubescent or villous along veins, margin denticulate to serrate. Corolla white or yellow. Staminode > 1 mm long. Abaxial stamens > 1.5 cm long. Ovary > 10 mm long 3
Stem sparsely puberulent or glabrescent. Leaf blades glabrous, abaxially sparsely puberulent along veins, margin denticulate to entire. Peduncle sparsely puberulent. Corolla white to yellow. Staminode ca. 0.5 mm long. Abaxial stamens ca. 1 cm long. Ovary 7–8 mm long. L. glabrifolium
3 Leaf blades abaxially reddish-purple, sparsely pubescent on both surfaces; lateral veins 11–19 pairs; petiole pubescent. Margin of bract denticulate. Corolla white to pale yellowish-white with purple-spotted inside, 3.7–3.8 cm long. Abaxial stamens 2–2.1 cm long. Staminode ca. 2 mm long. Ovary 1–1.2 cm long, densely glandular-puperulent L. puhoatense
Leaf blades green; adaxially appressed puberulent to pubescent, abaxially pubescent, villous along veins; lateral vein 6–10 pairs; petiole densely pilose. Margin of bract entire. Corolla yellow, inside spotted or not, 4–5 cm long. Abaxial stamens ca. 1.8 cm long. Staminode ca. 1 mm long. Ovary ca. 2 cm long, glabrous L. dongxingensis
4 Leaves ovate to broadly elliptic, margin repand to serrulate. Margin of bract denticulate to repand. Calyx ovate. Corolla white-lilac, inside purple spots and glabrous L. fimbrisepalum
Leaves elliptic to ovate or obovate, margin serrate to crenate-serrulate. Bract with irregularly dentate margin. Calyx broadly ovate or oblanceolate. Corolla yellowish, inside purplish to brownish spots and puberulent L. griffithii

Acknowledgments

The authors are indebted to the Management Board of Pu Hoat Nature Reserve, including Mr. Nguyen Thac Canh and Mr. Nguyen Dang Tung, for their support during the field trips. We also wish to thank Prof. Michael LoFurno, Temple University, Philadelphia PA, the USA for editorial assistance.

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