Syzygium ngheanense N.S.Lý, N.Đ.Đ

Lê, Th ị-Hương, Nguy ễn, Thành-Chung, Tr ần, Th ị-Thuý-Nga, Đ ỗ, Ng ọc-Đài & Lý, Ng ọc-Sâm, 2024, Syzygium ngheanense (Myrtaceae: Myrtoideae), a new species of Syzygium from Central Vietnam, Phytotaxa 641 (3), pp. 228-234 : 230-233

Syzygium ngheanense N.S.Lý, N.Đ.Đ ỗ & T.H.Lê sp. nov., ( Fig. 1 & 2 )

Diagnosis: —Most similar to S. vestitum , S. scabrum and S. levinei but differs by its light green with purplish-red tinge and sparsely scabrid flower buds and hypanthia (vs green and densely scabrid in S. scabrum , white and densely scabrid in S. levinei and S. vestitum ), glabrous bracts, bracteoles and sepals, larger sepals and petals, longer stamens and styles, fruit with surface rugose and foveolate ( Table 1 ).

Type: — VIETNAM. Nghe An Province: Que Phong District, Hanh Dich Commune, Pu Hoat Nature Reserve, 30 July 2021, 19 ° 24’43”N, 104 ° 49’28”E, elev. 757 m, Đỗ Ngọc Đài, Lê Thị HƯƠng, Nguyễn Thành Chung, DH 2021003 (holotype: VNM!, isotype: P).

Medium evergreen tree to 12 m tall with a straight bole, ca. 15 cm in diameter at DBH; branches spreading from upper trunk; no buttresses. Outer bark grey-white, smooth in young trees, irregularly fissured to longitudinally flaky in old trees; inner bark pale cream; wood cream-coloured; new flush of leaves and petioles light green, erect, sometimes spreading. Twigs terete, 2.5–3 mm in diam., covered with coarsely brownish hairs and scabrid, internode 1.4–6 cm long. Leaves simple, opposite, somewhat elliptic to ovate-elliptic, (3.6–)8–14.5 × (2.8–) 3.5–5.2 cm, chartaceous to subcoriaceous, apex acuminate, acumen to 1.8 cm long, base rounded or subcordate, margin entire, slightly recurved, adaxially dark green (brown when dried), smooth and shiny, glabrous, abaxially dull greenish (dark brown when dried), with densely gland dots (black when dried), glabrous except coarsely white scabrid on midrib; midrib sunken adaxially, prominent abaxially; lateral nerves (16–)21–27 pairs, 3–7.3(–9.5) mm apart, sunken adaxially, prominent abaxially, glabrous, inter-lateral nerves more or less distinct, prominent abaxially, intramarginal nerve 1, 1.5–2.5 mm from margin, prominent abaxially; petiole thick and robust, canaliculate, (2–) 3–5 mm long, 1.6–2 mm in diam., light green (dark brown when dried), densely scabrid as in twig. Inflorescence mostly terminal, sometimes axillary on leafy twig, paniculate-cyme, 3.5–9 cm long; peduncle 1.5–3 cm long, pale green to brownish-green, densely white hairs and scabrid, apex of terminal branches with 3 flowers. Flower buds obovoid, 5–6 mm long, 4–4.5 mm in diam., light green with purplish-red tinge at apex, sparsely scabrid. Hypanthium funnel-shaped, 6–7 mm long, 5–6 mm wide at apex, light green with purplish-red tinge (green after anthesis), sparsely scabrid; pseudostipe 1.5–1.8 × ca. 0.6 mm; bracts and bracteoles narrowly ovate, 1.5–3 mm long, ca. 0.5 mm wide at base, glabrous on both surfaces, apex acute, soon caducous. Sepals persistent, 4 or 5, free, triangular ovate, 3.4–3.8 × 1.1–1.8 mm, purplish-red (green after anthesis), finely gland dots, glabrous, apex rounded, margins entire. Petals 4 or 5, free, suborbicular, slightly concave, 3.6–4.8 × 3.2–4 mm, membranous, with 62–105 gland dots, white, glabrous, base truncate, apex rounded, soon caducous. Stamens numerous (ca. 162), white, glabrous; outer stamens 15–17 mm long, inner stamens 6–12 mm long; filaments cylindric, narrowed, with scattered gland dots; anthers oblong-ovate, 0.4–0.5 mm long, cream; anther sacs parallel, connective gland inconspicuous. Style 17–18 mm long, white, with scattered gland dots, glabrous. Ovary 2-locular, 8–10 ovules per locule, irregularly radiating. Mature fruits berry, somewhat globose, 1.7–3.2 × 1.8–3 cm, glabrous, surface rugose and foveolate; calyx ring 5–6 mm in diam., rim ca. 1.5–2 mm high. Seed 1, somewhat globose, 1.7–2 cm high, 1.6–2 cm in diam., dark brown, glabrous, intercotyledonary intrusion absent.

Phenology: —Flowering in June to August, fruiting in July to October.

Habitat and Ecology: —This new species grows along streams, in wet ground or on hill slopes in secondary evergreen broadleaved forests (Pu Huong NR) and mixed bamboo forests (Pu Hoat NR) at elevations of 300– 800 m.

Distribution and IUCN Preliminary assessment: — So far know only from two nature reserve areas in the Nghe An Province, north-central Vietnam. Currently, a single population of about 30 scattered mature plants was observed in Pu Hoat NR while less than 15 individual mature plants are found in Pu Huong NR. The two localities are distanced about 50 km from each other. The extent of occurrence (EOO) and area of occupancy (AOO) were estimated to be 69.4 km 2 and 8 km 2, respectively. The known habitat of the new species is well-protected within Pu Hoat and Pu Huong NRs, no specific threats are known. Based on currently available data, we provisionally assessed this species with a status of Endangered (EN B1, B2ab (ii, iii), D) according to IUCN Red List Criteria (IUCN, 2023). Further survey work in areas adjacent to Nghe An Province is required to better-access the distribution and conservation status of this species.

Etymology: —The specific epithet “ ngheanense ” denotes the geographic location, the Nghe An Province of Vietnam, where the new species was discovered.

Additional specimens examined (paratypes): — VIETNAM. Nghe An Province, Que Phong District, Hanh Dich Commune, Pu Hoat Nature Reserve , 05 September 2020, 19 ° 24’02”N, 104 ° 58’18”E, elev. 762 m, Đỗ Ngọc Đài, Lê Thị HƯƠng, Nguyễn Thành Chung, DH-2020016 ( VNM!) ; Quy Chau District, Dien Lam Commune, Cuom Village , Pu Huong Nature Reserve , 17 January 2021, 19 ° 23’54”N, 104 ° 57’37”, elev. 366 m, Đỗ Ngọc Đài, Lê Thị HƯƠng, DH-2021002 ( H!) ; 29 October 2022, 19 ° 42’43”N, 104 ° 49’28”E, elev. 541 m, Đỗ Ngọc Đài, Lê Thị HƯƠng, Nguyễn Thành Chung, Trần Thị Thuý Nga, DH-2022028 ( VNMN!) .

Taxonomic notes: — Including the present study, the number of Syzygium species in Vietnam increases to 53. The new species should be placed in subg. Syzygium by its persistent and free sepals, free petals, parallel anther sacs, nonfibrous hypanthium, axile-median placentation with irregularly radiating ovules and seed without intercotyledonary intrusion ( Craven & Biffin 2010). Syzigium ngheanense has somewhat elliptic leaves and scabrid-hairy inflorescences, funnel-shaped hypanthium and is thus morphologically similar to S. vestitum (from south western China (Yunnan Province), Laos (Vientiane) and Vietnam (North and Central regions)), S. scabrum (from Laos (Vientiane Province) and Thailand (Nakhon Phanom and Buengkan Provinces)), S. levinei ( Cambodia, southern China (Guangdong, Guangxi and Hainan Provinces, and Hong Kong)) ( Soh & Parnell 2015, Tagane et al. 2018). The major differences between S. ngheanense and the latter three are given in the above diagnosis. The somewhat scabrid twigs, leaves and inflorescences, and somewhat globose fruits in S. ngheanense most closely resemble those of S. vestitum and S. scabrum . However, the new species is distinguished from the latter two by its glabrous lateral nerves on abaxial surface of laminae and fruits with rugose and foveolate surface. The glabrous leaves and petioles and small ovoid fruits in S. levinei clearly distinguishes this species from the others. More detailed comparisons involving mainly morphological characters between the four hairy species of Syzygium in Indochina is presented in Table 1 , and a key to their recognition follows.

Figures

FIGURE 1. Syzygium ngheanense. A. Leafy twig with inflorescences.B. Leaf (abaxial view).C. Close-up of abaxial leaf.D. Inflorescence. E. Flower bud and its longitudinal section. F. Petals. G. Stamens. H. Infructescence with mature fruits. Drawn from type materials by Mrs. Phan Thị Thanh Nhã.

FIGURE 2. Syzygium ngheanense. A. Habit. B. Bole showing details of outer and inner barks (inset). C. Young twigs. D. Leafy twig with flowers after anthesis, close-up of abaxial leaf base (insit), and mature leaves. E. Inflorescences. F. Compound cyme with flowers at anthesis. G. Flower. H. Compound cyme with flowers after anthesis. I. Infructescences with mature fruits. J. Seed. Photos by N.-Đ. Đỗ, layout by N.-S. Lý.