Schizostachyum kohchangense 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 : 276-278

(10) Schizostachyum kohchangense W.Arthan, Teerawat. & Sungkaew , sp. nov.

Type: — THAILAND, Trat, Ko Chang , alt. 40 m, 12° 04’ 39” N, 102° 22’ 01’’ E, 13 August 2022, S. Sungkaew & A. Teerawatananon 1701 (holotype: BKF; isotypes: BK, Natural History Museum, Thailand). Figs. 1F–J & 4 .

Paratypes:— THAILAND, Trat, Ko Chang, alt. 31 m, 12°04’39.19” N, 102°22’01.42” E, 24 February 2024, S. Sungkaew & A. Teerawatananon 1829 (Thailand Natural History Museum).

Diagnosis: — Schizostachyum kohchangense is similar to S. aciculare but can be distinguished from the latter in its culm leaf auricles that are 3–5 mm high (in S. aciculare , they are just 1–2 mm high), almost glabrous pseudospikelets which are hairy only near the apex and the shorter floret which is 1.5–2 mm long. In S. aciculare , the floret is 2–3(–4) mm long and hairy all over. ( Table 1).

Description: — Culms erect, 5–15 m high, tips arching to drooping, occasionally scrambling or clambering on other vegetation; internodes dull green when young, light green to glaucous when mature, 40–100 cm long, 1–3.5 cm in diameter, covered with thin white wax and pale hairs, green and glabrous when mature; walls 2–3 mm thick; nodes without prominent nodal line, sparsely covered with short white to pale hairs around the node. Culm leaves: sheaths yellowish green to green throughout, 13–15 cm long, apex symmetrical, concave, base of outer margin without a projection, covered with pale to dark brown hairs on abaxial side; auricles conspicuously lobed, 3–5 mm high, 1–1.5 cm long, oral setae 0.5–1 cm long; ligules ca. 1 mm high, irregularly toothed, ciliolate; blades spreading, initially green, later yellowish green to straw-colored, sometimes brown at the base, lanceolate to ovate-lanceolate, 3.5–7 cm long, slightly constricted, glabrous on abaxial side, sparsely hairy on adaxial side. Foliage leaves: auricles inconspicuous lobes ca. 0.5 mm high, oral setae 1–1.5 cm long; ligules inconspicuous; blades 21–25.2 × 1.8–3.0 cm, glabrous on both sides. Pseudospikelets green to yellowish green, fusiform, 2.5–5 cm long; rachilla internodes (0.5–) 1–3.5 cm long; fertile florets solitary, 1.5–2 cm long, occasionally with terminal rachilla extension, 3–7 mm long, and with a vestigial floret to 1.5 cm long; lemmas convolute, 1.2–1.6 cm long, hairy near the apex; paleas convolute, 1.5–1.8 cm long, slightly keeled, glabrous. Lodicules absent. Stamens: anthers yellow to purple, 5–7 mm long; filaments free.

Distribution and ecology: — Schizostachyum kohchangense is, so far, only known from Trat Province in southeastern Thailand and grows in shady areas and along streams in evergreen forests.

Conservation status: — Schizostachyum kohchangense has a small EOO of less than 5,000 km 2 (232.1 km 2) which places it in the Endangered (EN) conservation category and a small Area of Occupancy (AOO) of less than 500 km 2 (64.0 km 2) that also results in EN category. This bamboo is exclusively found on Ko Chang (Chang Island) in Trat Province, South-Eastern Thailand, which can be regarded as a single location with severely fragmented natural vegetation. Based on IUCN (2023) criteria, S. kohchangense is therefore assessed as Endangered [EN B1, B2a].

Vernacular name: —ไผ่กะแสนเขียว (Phai Kasaen Khiao).

Etymology: —The specific epithet ‘ kohchangense ’ refers to Koh Chang National Park (Chang Island) where this species was first collected and described. We adopted ‘ kohchangense ’ as it is used in other taxa (as ‘ kohchangensis’) and contains the old transliteration of the word ‘Koh’ (meaning island) which was widely used in the past; however, the word ‘Ko’ also appears in the literature.

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 4. (A–E) Schizostachyum nigrum W.Arthan, Teerawat. & Sungkaew, sp. nov. (A) Young culm shoot; (B) Two young culms showing prominent projection at the base of outer sheath margin (left) and nodes with a ring of hairs (right); (C) Leafy branch; (D) Branch complement with several slender subequal branches per node; (E) Flowering branches. (Illustrated by W.Bhuchaisri, all from S. Sungkaew & A. Teerawatananon 1708, Thailand Natural History Museum).