Research Article |
Corresponding author: Shuichiro Tagane ( stagane29@gmail.com ) Academic editor: Irina Belyaeva
© 2016 Shuichiro Tagane, Viet Hung Nguyen, Nguyen Van Ngoc, Hoang Thanh Son, Hironori Toyama, Chen-Jui Yang, Tetsukazu Yahara.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Tagane S, Nguyen VH, Ngoc NV, Son HT, Toyama H, Yang C-J, Yahara T (2016) Homalium glandulosum (Salicaceae), a new species from Vu Quang National Park, North Central Vietnam. PhytoKeys 58: 97-104. https://doi.org/10.3897/phytokeys.58.6816
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Homalium glandulosum Tagane & V. H. Nguyen, from Vu Quang National Park in northern Vietnam, is newly described. This species is characterized by distinct glands, often stalked, at the base of the lamina and along the margin of the stipules and bracteoles. Illustrations, DNA barcodes of the two regions of rbcL and matK, and a key to the species of Homalium in Vietnam are also provided.
Homalium , new species, Salicaceae , taxonomy, Vietnam, Vu Quang National Park
Homalium Jacq., with more than 150 species, is a genus of woody plants widely distributed in the tropics of the world, with the center of diversity in Southeast Asia and Madagascar (
In Vietnam, 11 species of Homalium have been known: H. caryophyllaceum (Zoll. & Moritz) Benth., H. ceylanicum (Gardner) Benth. (synonym, H. balansae Gagnep., H. hainanense Gagnep.), H. cochinchinense (Lour.) Druce (synonym, H. digynum Gagnep., H. fagifolium (Lindl.) Benth.), H. dasyanthum (Turcz.) W. Theob. (synonym, H. griffithianum Kurz), H. dictyoneurum (Hance) Warb., H. grandiflorum Benth., H. mollissimum Merr., H. myriandrum Merr., H. petelotii Merr., H. phanerophlebium F. C. How & W. C. Ko, and H. tomentosum (Vent.) Benth. (
Vu Quang National Park covers an area of ca. 56,000 ha containing an elevation gradient of over 2,000 m, from 30 m in the lowlands to 2,286 m at the summit of Mt. Rao Co (Rào CÓ), on the border with Laos (
During our botanical inventory in Vu Quang National Park in July 2015, we discovered a previously undescribed species of the genus Homalium. Here we describe the species as H. glandulosum, accompanied with illustrations, DNA barcodes of the two plastid regions rbcL and matK (
Similar to H. petelotii Merr., but differing in having distinct glands, often stalked, at base of lamina and along margin of stipules and bracteoles, and spreading hairs on rachis of inflorescences, calyx tubes, sepals and petals (vs. glabrescent or only short appressed hairs in H. petelotii). Also, similar to H. cochinchinense (Lour.) Druce and H. mollissimum Merr. but distinguished from these two by the distinct glands mentioned above and very sparsely pubescent branches and petioles (vs. pubescent to densely pubescent).
VIETNAM. Ha Tinh Province; Vu Quang National Park; along the trail to the summit; in hill forest, alt. 453 m, 18°16'25.3"N, 105°21'40.8"E, 25 July 2015, Tagane S., Yahara T., Toyama H., Nguyen N., Yang C. J. & Nguyen H. V3735 (holotype KYO!; isotypes BKF!, DLU!, FU!, NTU!, the herbarium of Vu Quang National Park!).
Small tree, 9 m tall, DBH 15.6 cm; bark gray-brown; branchlets very sparsely pubescent, soon glabrous, with many lenticels, which are narrow to broadly elliptic, 0.3–0.9 × 0.1–0.25 mm, whitish; young twigs blackish when dry, old twigs grey-brown. Leaves: simple, alternate, petiole 2.5–5 mm long, sparsely pubescent when young, blackish when dry; leaf blade ovate to elliptic-ovate or oblong-ovate, (2.4–)3.5–9.8 × (1.0–)1.2–3.1 cm, papery, very sparsely pubescent on both surfaces, apex acuminate to acute, rarely obtuse, with a gland on tip, base cuneate, with 2–5 pairs of stalked glands at border with petiole, margin crenulate with glandular teeth; midribs prominent on both surfaces, glabrescent, secondary veins 6–7 pairs, arising at an angle of 40–45 degrees from the midrib, slightly prominent on both surfaces, tertiary veins reticulated, visible when dry. Stipules narrowly triangular, ca. 5 × 1 mm, thinly papery, with 4–6 glandular teeth per side, glands often stalked, apex acute, with a gland on tip, blackish when dry, very sparsely pubescent, caducous. Inflorescences axillary, pendant, racemes or racemiform panicles with flowers borne singly on rachis or in clusters of up to 3 sometimes on short branches, 4–9 cm long, 7–20 flowered; rachis densely pubescent with spreading hairs except glabrous and lenticellate basally; bracts caducous, not seen. Pedicels 2.5–3.5 mm long, densely pubescent with spreading hairs; bracteoles narrowly ovate, 2.5–3 mm long, margin with 3–5 stalked glands per side, glabrous except near base, caducous. Flowers fragrant, 6–8 mm in diam.; calyx tube ca. 2.5 mm long, densely pubescent with spreading hairs; sepals 8, narrowly oblanceolate, ca. 3 × 0.5 mm long, membranous, with conspicuous midvein, light green in vivo, glabrescent except near basal part on both surfaces and ciliate margin, hairs spreading, 0.6 mm long, apex apiculate, with a gland on tip; petals 8, oblanceolate, 3.5 × 1.1 mm, membranous, with conspicuous midvein and lateral veins, whitish in vivo, glabrescent except lower 1/3 on both surfaces, margin ciliate with spreading hairs, hairs ca. 0.6 mm long, apex obtuse to acute. Disk glands 8, ca. 0.3 mm in diam., orange in vivo, black when dry, stipitate, stalk ca. 0.15 mm long, sparsely hairy. Stamens 8, filaments ca. 5.5 mm long, sparsely spreading hairy in lower 3/5; anthers ca. 0.4 mm long, longitudinally and extrorsely dehiscent. Ovary semi-inferior. Styles 3 or 4, filiform, ca. 5 mm long, united in lower 1/3, hairy in lower 1/2, hairs spreading; placentas 3 or 4, each with (3–)4 ovules, sparsely hairy inside. Fruits not seen.
So far known only from the type locality.
Rare in hill evergreen forest, at alt. 453 m. Flowering specimens were collected in July.
Tagane et al. V3735: LC0901208 (rbcL), LC0901207 (matK). The BLAST similarity search based on the matK sequence of H. glandulosum resulted in homology as high as 834/835, 773/774, 767/768 bp with the sequence of H. cochinchinense (GenBank accession no. HQ415362, KP093841, KP093840, respectively) in the DNA database.
The specific epithet ‘glandulosum’ reflects the existence of distinct glands, often stalked, on stipule, leaf base and bracts.
Data Deficient. Only one flowering individual was found in a protected area of Vu Quang National Park. Further efforts for finding additional individuals/populations are needed to evaluate its conservation status.
In Vu Quang National Park, another species of Homalium, H. cochinchinense, occurs in lowland forest (e.g., alt. 70 m, 27 July 2015, Tagane et al. V3818 (
1a | Stamens solitary before each petal | 2 |
1b | Stamens 2 or more before each petal | 8 |
2a | Styles dentiform, less than 1 mm long | H. tomentosum |
2b | Styles filiform, 2–5 mm long | 3 |
3a | Petals less than 2 mm long | H. ceylanicum |
3b | Petals 3–4 mm long | 4 |
4a | Stipules, leaf bases and bracts with stalked glands | H. glandulosum |
4b | Stipules, leaf bases and bracts without stalked glands | 5 |
5a | Petioles 8–15 mm long; leaves with acumen ca. 10 mm or more; leaf blade drying blackish brown | H. phanerophlebium |
5b | Petioles less than 7 mm long; leaves with acumen 9 mm or less; leaf blade not drying blackish (i.e. reddish brown to dark greyish brown) | 6 |
6a | Inflorescences glabrescent or pubescent only with short appressed hairs | H. petelotii |
6b | Inflorescences pubescent with spreading trichomes | 7 |
7a | Abaxial surface of leaf pubescent on midrib and lateral veins only | H. cochinchinense |
7b | Abaxial surface of leaf sparsely to densely pubescent throughout | H. mollissimum |
8a | Stamens partly inserted on the lower part of the petals; sepals manifestly accrescent after anthesis | 9 |
8b | Stamens inserted strictly between the disk glands; sepals not or slightly accrescent after anthesis | 10 |
9a | Bracts lanceolate-oblong, 4–8 mm long, caducous | H. grandiflorum |
9b | Bracts ovate-flabelliform, 5–6 mm long, persistent | H. dictyoneurum |
10a | Stamens consistently 2 before each petal | H. dasyanthum |
10b | Stamens at least partly in fascicles of 3 or more | 11 |
11a | Flowers with distinct pedicles of 3–5 mm long; calyx tube same length as the petals | H. myriandrum |
11b | Flowers subsessile; calyx tube more than twice as long as petals | H. caryophyllaceum |
The authors cordially thank the Vietnam Administration of Forestry and Vu Quang National Park for permitting our botanical inventory in the protected area. We thank the curators and staff of