Gigantochloa sp. (TH: Chumphon)

Specimen: BS-0087 [E1] (living plant), อำเภอพะโต๊ะ, Pha To District, Chumphon, southern Thailand, coll. C. S., received 27 July 2012.

Characteristics: Habit moderately tight caespitose, with culms ca. 10–20 cm apart. Rhizome pachymorph, short. Culms straight, more or less erect, over 10 m tall [ultimate height not yet known]. Young shoots conical, light green with yellowish green stripes, glabrous; sheath margins green, eciliate; culm-leaf blades reflexed and green; emerge from May/June. Culm-internodes terete, 26–37 cm long, medium to dark green, the basal and lower culm green with narrow stripes in yellowish to yellowish green, or, in mature clumps, yellowish green with narrow stripes in medium green; initially with scattered short rigid whitish hairs, becoming glabrous soon, not farinose; diameter to ca. 10 cm; walls thick, the lacuna diameter about equal to wall width at ca. 1 m height above the ground, solid on the basal culm. Culm-nodes glabrous, smooth, not prominent; nodal line horizontal; sheath scar not protruding; supranodal line obscure, without ridge; aerial roots possibly present in mature culms; short root primordia present on the basal and lower nodes of mature culms. Branch-buds solitary, subrotund to dome-shaped to triangular, from the basal node up. Branches several, unequal, the central one dominant; branching from the lower culm or mid-culm up, unbranched on the basal culm; branching intravaginal; branching development basipetal (apex towards the base); rebranching. Culm-leaves late deciduous on the lower culm, early deciduous on the branched nodes of the mid-culm and upper culm. Culm-leaf sheaths parabolic, about one-fifth taller than the basal width; the sheath length shorter than the internode length, about one-third of the internode on the lower culm; rigid, brittle, light green with narrow whitish to yellowish green stripes when young, light straw-colored with a tinge of red or pinkish when dry; covered with short rigid appressed caducous whitish hairs when young, soon becoming glabrous but not smooth, not farinose; apex convex-rounded; margins eciliate. Culm-leaf auricles low erect glabrous, entire rims, adnate to the margins of the blade base and extending along the sheath apex but not reaching the sheath margins, dark green when young. Culm-leaf ligule low, ca. 1 mm high, dark colored; margin erose or irregularly toothed, initially with early caducous short pale rigid bristles. Culm-leaf blades leathery, usually persistent, deflexed to reflexed, triangular, green on both surfaces, rather short, less than half the length of the sheath length on the mid-culm, less than 1/4 on the lower and basal culm; the width of the junction with the sheath nearly as broad as the blade base; adaxially densely pale hairy from the base to ca. 1/3 of the blade length, otherwise glabrous including the margins, abaxially glabrous throughout; becoming light straw-colored when dry; apex long acuminate, sharp-pointed; margins eciliate, incurved when dry. Foliage-leaves (6) 7–13 per branchlet. Foliage-leaf sheaths keeled on the back, light green when young, initially with short pale hirsute or appressed hairs, becoming glabrous soon; apex convex-truncate, reddish when young; margins eciliate. Foliage-leaf auricles tiny rounded erect lobes, ca. 1/2 mm high, glabrous, entire. Foliage-leaf ligule low, ca. 1 mm high, glabrous, margin denticulate or entire; outer ligule a low glabrous rim. Foliage-leaf blades thin, somewhat rigid, lanceolate, 16–27 (36) × 2–3.5 (4.5) cm, glabrous on both surfaces, medium green; base rounded to short-attenuate; apex acuminate to attenuate; margins antrorsely scabrous; midrib distinct, proximally prominent and light green beneath; pseudopetiole short, 1–3 mm long. Flowers and seeds are unknown.

Provisional identification: A species of Gigantochloa. The plant collector assumed that this species might be Gigantochloa scortechinii, but their vegetative characteristics are too different. However, similarities in the characteristics could be found in the unidentified Gigantochloa species of BS-0601, BS-0434, and BS-0635. Their characteristics should be re-examined and compared with each other when the plants are fully grown in a few years.