Vietnamosasa sp. (TH: Nong Khai)

Specimens: BS-0586 [S3] (living plant), banks of Mekong River, in อ. ท่าบ่อ (Tha Bo District) or adjacent อ. ศรีเชียงใหม่ (Si Chiang Mai District), Nong Khai Province, north-eastern Thailand, wild, 1–2 m tall, on open site, in association with a flowering panicoid grass species, coll. by ธ. ล., received as "ไผ่โจด" (phai chot), Nov. 2010.

Characteristics: Habit tight pluri-caespitose, bushy. Rhizome leptomorph. Culms straight, erect and bending, bending outwards down to the ground, 1.6 m long. Young shoots emerge from March to October. Culm-internodes terete, 17–22 cm long, mid-green, glossy when young, glabrous, smooth, not farinose, diameter 0.2–0.35 cm; walls about 0.7 mm thick in culms with diameter 2 mm, lacuna filled with white pith, the basal culm almost solid. Culm-nodes glabrous, smooth, slightly prominent; sheath scar about 1 mm high and 0.5 mm protruding, supranodal line indiscernible; without a white ring below sheath scar; aerial roots none. Branch-buds solitary, from the basal node up, very tall (10 mm high in culms with diameter of 2–3 mm). Branches 1–2 to several to many, the first branch slightly less slender than the main culm, present from the basal or lower culm up; branching intravaginal; rebranching. Culm-leaves deciduous. Culm-leaf sheaths 4–5 cm long, about 1/4 of the internode length, papery, brittle, glabrous, smooth, mid-green when young, light straw-colored when dry; outer margin densely short whitish ciliate [inner margin not seen]; apex rounded. Culm-leaf auricles inconspicuous tiny outwards tilted lobes, with short whitish caducous bristles 1–3 mm long. Culm-leaf ligule inconspicuous, 0.5 mm high, entire or denticulate. Culm-leaf blades papery, mid-green when young, light straw-colored when dry, persistent or occasionally caducous, erect on the basal culm, deflexed to reflexed on the lower to upper culm, triangular on the basal culm, triangular with rounded basal edges on the lower and upper culm, less than half the length of the sheath on the basal culm; apex long pointed. Foliage-leaves 5–8 per branchlet. Foliage-leaf sheaths not keeled, mid-green when young, light straw-colored when dry, glabrous; outer margin densely short whitish ciliate [inner margin not seen]. Foliage-leaf auricles inconspicuous tiny outwards tilted and protruding lobes, with a few short whitish late caducous patent bristles 3–6 mm long. Foliage-leaf ligule inconspicuous, 0.5 mm high, entire or denticulate; outer ligule none. Foliage-leaf blades soft when young, almost tough when old, 13–30 (33) × 0.7–1.2 cm, glabrous on both surfaces, dark to mid-green above, pale green beneath, linear; base rounded; apex long pointed; margins antrorsely scabrous; midrib proximally slightly prominent beneath; veins 4–5 pairs, not tessellate; pseudopetiole very short, 0.5 mm long or sessile. Flowers and seeds are unknown.

Provisional identification: BS-0586 is obviously a species of Vietnamosasa, but its characteristics do not fit well with Vietnamosasa ciliata or Vietnamosasa pusilla. The main differences are the much longer foliage-leaf blades in BS-0586, which are linear with a rounded base, glabrous on both surfaces, and venation is not tessellated (leaf blade assessed at 45× magnification).