Syzygium yersinii Tagane, V.S.Dang & Yahara, 2018

Tagane, Shuichiro, Dang, Van-Son, Souladeth, Phetlasy, Nagamasu, Hidetoshi, Toyama, Hironori, Naiki, Akiyo, Fuse, Kengo, Tran, Hop, Yang, Ceng-Jui, Prajaksood, Amornrat & Yahara, Tetsukazu, 2018, Five new species of Syzygium (Myrtaceae) from Indochina and Thailand, Phytotaxa 375 (4), pp. 247-260 : 255-257

Syzygium yersinii Tagane, V.S.Dang & Yahara , sp. nov. ( Figure 6 ).

TYPE:— VIETNAM. Khanh Hoa Province, Mt. Hon Ba, 12°06′46.88″N, 108°58′14.43″E, elev. 919 m, 19 Feb. 2014, Toyama H., Dang V.S., Tagane S., Fuse K., Yahara T., Nagamasu H., Tran H., Nguyen V.N., Nguyen Q.C., Do N.T. & Ho N.P.H. V786 [fl. bud] (holotype KYO!, isotypes FOF!, KAG!, VNM!, the herbarium of Hon Ba Nature Reserve).

Syzygium yersinii is similar to S. chantaranothaianum Soh & Parnell (2012: 558) in ovate-oblong leaf shape, very short petioles and terminal inflorescences but differs in having larger and thicker leaves (thickly coriaceous in S. yersinii vs. subcoriaceous in S. chantaranothaianum ), reticulate tertiary vein (vs. scalariform) and larger flowers (hypanthium 1.8 cm long vs. 0.8–1 cm long).

Shrubs, 4 m tall. Young twigs terete, yellowish brown to grayish brown, glabrous, old twigs grayish brown to very pale creamy brown, glabrous, internode 2–13 cm long. Leaves opposite, blade ovate-oblong, 12.2–21.4 × 5.4–8.3 cm, 1.8–2.9 times longer than wide, thickly coriaceous, apex acuminate, acumen to 1.2 cm long, base slightly cordate to cordate, margin entire, recurved when dry, glabrous, midrib sunken adaxially, prominent abaxially, secondary veins 20–24 pairs, 0.6–1.5 cm apart, prominent and distinct on both surfaces, intersecondary veins prominent and distinct on both surfaces, tertiary veins reticulate, prominent on both surfaces, intramarginal veins 2, outer one ca. 0.6 mm apart from margin, inner one 2–3.5 mm apart from margin; petiole to 1.3 mm long, blackish when dry, glabrous. Inflorescence terminal, racemose, 3 to 5-flowered, peduncle 3 mm long, glabrous, bracteoles caducous, not seen. Flower buds ca. 2.2 cm long, 1.1 cm in diam., light yellowish green (in vivo). Hypanthium funnel shaped, ca. 1.8 cm long, glabrous, pseudostipe 4–7 mm long. Sepals 4, semi-circular, 4–5 × 6–8 mm, petals 5–6, orbicular, depressed ovate, depressed obovate, 7–10 × 7–14 mm, white (in vivo), chartaceous, with many glands. Stamens more than 480, 2–10 mm long, anthers 1–1.2 mm long, filaments 1.8–9 mm long, glabrous. Style 1.1–1.3 cm long, glabrous (floral measurements were made from rehydrated flower buds). Ovary 2-locular, ovules 8–10 per locule. Fruits globose, ca. 3.2 cm in diam., Seed 1, subglobose, 2.2 cm in diameter.

Paratypes: — VIETNAM. Khanh Hoa Province: Mt. Hon Ba, 12°06′51.31″N, 108°58′23.34″E, elev. 890 m, 21 July 2013, Tagane et al. V638 [fr.] (FU!, VNM, the herbarium of Hon Ba Nature Reserve ) ; 12°06′46.88″N, 108°58′14.43″E, elev. 919 m, 20 Feb. 2014, Toyama H., Dang V.S., Tagane S., Fuse K., Yahara T., Nagamasu H., Tran H., Nguyen V.N., Nguyen Q.C., Do N.T. & Ho N.P.H. V 750 [ster.] (FU!, VNM, the herbarium of Hon Ba Nature Reserve ) .

Distribution:— Vietnam (so far only known from the type locality, Mt. Hon Ba).

Habitat and Ecology:— Hill evergreen forest, at 890–920 m elevation.

Phenology:— Flowering specimens collected in February.

Etymology:— This species is named after Dr. Alexandre Emile Jean Yersin (1863–1943), a Swiss-French, for his contributions to the exploration of the Hon Ba mountain.

Vernacular name:— Trâm yersin.

Preliminary conservation assessment:— Endangered (EN). According to our observations in the field in Mt. Hon Ba and its adjacent areas (six times, from lowland to the summit of Mt. Hon Ba (ca. 1560 m elev.) in 2013–2017), Syzygium yersinii is endemic to Mt. Hon Ba and known only from the narrow range of Mt. Hon Ba, around 900 m elevation. We estimate the number of mature individuals to be fewer than 150, suggesting the situation is qualified as EN according to IUCN Red List criteria D ( IUCN 2012). The forest in Hon Ba Nature Reserve is currently well protected from anthropogenic activities and therefore the population is seemingly stable.

Note:— Lee et al. (2014: 398) identified this species as Syzygium formosum ( Wallich 1831: 108) Mason (1851: 554) but S. yersinii is easily distinguished from S. formosum by its opposite leaves (vs. usually whorled in S. formosum ) and terminal inflorescences (vs. in the axils of fallen leaves). The leaf texture and venation when dry is very similar to S. grande ( Wight 1841: 17) Walpers (1843: 180) , but differs from S. grande in its small habit (4 m tall vs. usually more than 20 m tall), subsessile leaves (vs. petiolate in S. grande ) and more or less slightly cordate leaf base (vs. cuneate).

Figures

FIGURE 6. Syzygium yersinii Tagane, V.S.Dang & Yahara.A) Branch with flower buds, B) Portion of lower leaf surface, C) Flower buds, D) Fruit, E) Petals, F) Stamens, G) Dissected hypanthium showing style. Photographs: A–C for Toyama et al. V786, taken by K. Fuse on 20 Feb. 2014; D for Toyama et al. V638, taken by S. Tagane on 21 July 2013; E–G from Tagane et al. V786 (KAG). Scale bars E = 1 cm, F & G = 5 mm.