Syzygium phoukhaokhouayense Soulad., Tagane & 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 : 253

Syzygium phoukhaokhouayense Soulad., Tagane & Yahara , sp. nov. ( Figure 4 ).

TYPE:— LAOS. Vientiane Province, Thoulakhom district, Ban Pa Paek, Phou Khao Khouay National Protected Area, 18°22′35.28″N, 102°51′29.46″E, 905 m elev., 26 December 2017, Yahara T., Tagane S., Souladeth P., Nagamasu H., Naiki A., Chayer S. & Kongxaisavath D. L1827 [fl.] (holotype FOF!, isotypes BKF, KAG, KYO!, NHL!, P).

Syzygium phoukhaokhouayense is similar to S. syzygioides ( Miquel 1855: 431) Merrill & Perry (1938: 109) but differs in having coriaceous leaves (vs. chartaceous to subcoriaceous in S. syzygioides ), longer petiole (7–12 mm long vs. 3–5 mm long), larger and reddish-purple hypanthium (4.1–4.5 mm long vs. ca. 3 mm long, greenish), longer styles (ca. 5 mm long vs. ca. 8.3 mm long) and fewer ovules per locule in ovary (4–5 per locule in S. phoukhaokhouayense vs. 10–14 per locule in S. syzygioides ). Also, it is apparently similar to S. lineatum ( De Candolle 1828: 287) Merrill & Perry (1938: 109) but easily distinguished by having more secondary veins (28–32 pairs in S. phoukhaokhouayense vs. 16–20 pairs in S. lineatum ) and single intramarginal veins (vs. 2).

Tree, 6 m tall. Young twigs terete, reddish brown, glabrous, 2–2.5 mm in diam., old twigs grayish to reddish brown, internode (1–) 2–3.6 cm long. Leaves opposite, blade elliptic to elliptic-oblong, 4.2–8.9 × 1.8–3.2 cm, 2.3–3.1 times longer than wide, coriaceous, reddish brown dark grayish brown adaxially, light yellowish brown abaxially, glabrous on both surfaces, apex acuminate, acumen to 1 cm long, base cuneate to attenuate, margin entire, slightly recurved when dry, midrib sunken abaxially, prominent and distinct adaxially, secondary veins 28–32 pairs, 1.5–2.8 mm apart, slightly prominent on both surfaces, intersecondary veins distinct, intramarginal veins 1, ca. 0.8 mm from margin; petiole 0.7–1.2 cm long, concave adaxially, rounded abaxially, blackish, glabrous. Inflorescences terminal and axillary near the top of branch, paniculate, 2.5–3.8 cm long, 8–40 flowered, peduncle up to 2.7 cm long, rachis and lateral branches compressed or slightly angled; bracteoles triangular, ca. 0.9 mm long, glabrous, caducous. Flower buds ca. 2.1 mm in diam., whitish to purplish (in vivo). Hypanthium funnel-shaped or campanulate, 4.1–4.5 mm long, blackish when dry, glabrous, pseudostipe ca. 2 mm long. Sepals 4, depressed semi-circular, 0.5 × 1.6 mm, petals 4, orbicular, ca. 2.4–3 mm in diam., membranous, gland dot lacking or 1 per petal. Stamens 30–32, 5.1–8.2 mm long, anthers ca. 0.4 mm long, filaments white (in vivo). Style ca. 8.3 mm long. Ovary 2-locular, ovules 4–5 per locule. Fruit and seeds not seen.

Distribution:— Laos (so far only known from Phou Khao Khouay National Protected Area).

Habitat and Ecology:— Open pine forest, at 905 m elevation.

Phenology:— Flowering specimens were collected in December.

DNA barcodes:— LC381851 (rbcL), LC381854 (matK); sequenced from Tagane et al. L1827.

Etymology:— The species epithet refers to the geographical location of the find, Phou Khao Khouay National Protected Area.

Vernacular name:—ຫວາພ (Wa Phou).

Preliminary conservation assessment:— Critically Endangered (CR).At present, Syzygium phoukhaokhouayense is known from only a single individual in the Phou Khao Khouay National Protected Area, at 905 m elev. The area is close to the Vientiane Capital, and has been relatively intensively surveyed by many botanists (e.g. Newman et al. 2007, Souladeth & Meesawat 2012, Lucas et al. 2013). However, we could not find any specimen of this species in the major herbaria (BKF, FOF, HN, KAG, NHL, P, RUPP, TNS, VNM), indicating that this is a rare species. This situation is qualified as CR according to IUCN Red List criteria D ( IUCN 2012).

Note:— The matK sequence of S. phoukhaokhouayense is identical with S. syzygioides (783/783 bp for GenBank accession no. AB924771 and AB925281, 780 bp for AB924710 and AB924734, 768/768 bp for AB924947). However, S. phoukhaokhouayense is easily distinguished from S. syzygioides by the diagnostic characters mentioned above, such as the differences in leaf thickness, length of petiole and style, and colour of hypanthium.

Figures

FIGURE 4. Syzygium phoukhaokhouayense Soulad., Tagane & Yahara. A) Flowering branch, B) Portion of lower leaf surface, C) Bark, D) Young shoot, E & F) Flowers. Photographs: A–F for Yahara et al. L1827, taken by S. Tagane on 26 Dec. 2017.