Schizostachyum nigrum W.Arthan, Teerawat. & Sungkaew, 2024

Sungkaew, Sarawood, Wong, Khoon Meng, Hodkinson, Trevor R., Thammanu, Siriluck, Cheysawat, Somboon & Teerawatananon, Atchara, 2024, Taxonomic revision of the bamboo genus Schizostachyum (Bambusoideae: Melocanninae) in Thailand, with two new species and five new records, lectotypifications and nomenclatural corrections, Phytotaxa 676 (3), pp. 263-286 : 279-280

(12) Schizostachyum nigrum W.Arthan, Teerawat. & Sungkaew , sp. nov.

Type: — THAILAND, Bueng Kan, Seka , alt. 250 m, 18° 9’ 12.73” N, 103° 57’ 5.64” E, 26 July 2010, S. Sungkaew & A. Teerawatananon 1207 (holotype: BKF; isotypes: BK, BKF, Thailand Natural History Museum). Figs. 1N–P & 5 .

Paratypes:— THAILAND, Buengkan, Bung Khla, alt. 326 m, 18°14’41.6” N, 103°57’29.1” E, 24 September 2022, S. Sungkaew & A. Teerawatananon 1708 (Thailand Natural History Museum).

Diagnosis: — Schizostachyum nigrum closely resembles S. cambodianum but the new species is distinguished from the latter ( Table 1) and other small Schizostachyum species by a set of morphological characters, namely: well-raised culm leaf sheath shoulders, suborbicular basal leaf sheath projection and rings of deciduous hairs at the node which are uncommon among Schizostachyum species.

Description: — Culms erect, 5–6 m high, tips drooping; internodes light to dull green throughout, 45–100 cm long, 1–2.5 cm in diameter, slightly swollen near base, initially less hairy, later with white to pale brown hairs; walls 1–1.5 mm thick; nodes with prominent nodal line, nodal line horizontal, slightly bigger than the adjacent internodes, with a ring of yellowish brown to brown hairs. Culm leaves: sheaths initially green, later purplish green, with light brown marginal area on both sides, 13–20 cm long, apex asymmetrical, concave, base of outer margin with a prominent projection, projection suborbicular, 0.6–1 cm wide, margins scarious, covered with brown to black hairs on abaxial side; auricles inconspicuous, oral setae 7–8 mm long; ligules ca. 0.5 mm high, irregularly toothed, ciliolate; blades deflexed, initially yellowish green to green towards the base, later green to purplish green, narrowly lanceolate, up to 20 cm long, usually glabrous on both sides. Foliage leaves: auricles inconspicuous, oral setae 5–6 mm long; ligules up to 0.5 mm high, irregularly toothed, ciliolate; blades 11–15 × 0.9–1.1 cm, glabrous on both sides. Pseusospikelets green, narrowly fusiform, 1.5–3.0 cm long; rachilla internodes 0.5–1.2 cm long; fertile florets solitary, 1.5–1.8 cm long, sometimes with a very short terminal rachilla extension ca. 2 mm long, without a terminal vestigial floret; lemmas convolute, 0.9–1.5 cm long, glabrous; paleas convolute, 1.4–1.8 cm long, not keeled, glabrous. Lodicules absent. Stamens: anthers yellow to purplish, 6–7 mm long; filaments free.

Distribution and ecology: — Schizostachyum nigrum is so far appear to be endemic to Thailand and only occurs in Seka, Bueng Kan Province. It grows in semi-evergreen forests.

Additional specimens examined: — THAILAND: South-eastern. Buengkan, Seka, 13 August 2004, S. Sungkaew & A. Teerawatananon 186 (Thailand Natural History Museum); Bung Khla, 29 May 2022, S. Sungkaew & A. Teerawatananon 1691 (Thailand Natural History Museum); the same locality, 24 September 2022, S. Sungkaew & A. Teerawatananon 1701 (Thailand Natural History Museum).

Conservation status: — Schizostachyum nigrum has a small EOO of less than 5,000 km 2 (180.3 km 2) which places it as Endangered (EN). Its small AOO of less than 500 km 2 (68.0 km 2) also qualifies it as EN. In addition, the populations were found in less than five locations. According to IUCN (2023) criteria, it is evaluated that the conservation status of S. nigrum is Endangered [EN B1, B2a].

Vernacular name: —ไผ่กะแสนดำ (Phai Kasaen Dam).

Etymology: —The specific epithet ‘ nigrum ’ is a Latin word meaning black characterizing the dense black hairs on the culm leaf sheath, especially on a young shoot.

Figures

FIGURE 1. (A–E) Schizostachyum aciculare Gamble. (A) Young culm showing culm leaf sheath, node and parts of internodes; (B) Culm leaf sheath apex; (C) Young culm shoot; (D) Part of leafy branch; (E) Flowering branches. (F–J) S. kohchangense W.Arthan, Teerawat. & Sungkaew, sp. nov. (F & J) Young culms showing culm leaf sheaths; nodes and parts of internodes; (G) Young culm shoot; (H) Part of leafy branch; (I) Flowering branches. (K–M) S. cambodianum Merkl., Chhang & K.M.Wong. (K) Young culm showing culm leaf sheath, nodes and parts internodes (note basal projection from the outer margin of the culm sheath proper); (L) Flowering branch; (M) Close-up of culm node with primary branch bud. (N–P) S. nigrum W.Arthan, Teerawat. & Sungkaew, sp. nov. (N) Flowering branch; (O) Close-up of culm node with the characteristic ring of hairs; (P) Young culm showing culm leaf sheath (note basal projection of outer margin), node and parts internodes. (Photographed by A. Teerawatananon & D. Pathumthong).

FIGURE 5. (A–D) Schizostachyum kohchangense W.Arthan, Teerawat. & Sungkaew, sp. nov. (A) Young culm shoot; (B) Young culm with culm leaf attached; (C) Culm leaf, abaxial view; (D) Flowering branch. (Illustrated by W. Bhuchaisri, all from S. Sungkaew & A. Teerawatananon 1701, Thailand Natural History Museum).