Gigantochloa sp. (AU)

Specimen: BS-0507 [C7n] (living plants), Queensland, Australia, cult., received as "Gigantochloa ridleyi with curved culms", 7 June 2010.

Images: Photos in JanneNilsson (shoots etc.).

Characteristics: Habit tight caespitose. Rhizome pachymorph, short-necked [n.v.]. Culms straight, erect, bending outwards above, over 10 m tall [ultimate height not yet known]. Young shoots light green, with streaked light green erect to patent culm-leaf blades, with patches of dark hairs; emerge from April to September. Culm-internodes terete, 31–30 cm long, dull mid-green to dark green, somewhat rough on the upper third, otherwise glabrous and smooth, not farinose, diameter 6.5 cm [ultimate diameter not yet known]; walls [not yet observed]. Culm-nodes glabrous, smooth, flat; sheath scar marginally protruding; supranodal line discernible, without a ridge, 5–8 mm above the nodal line; aerial roots on the basal nodes present. Branch-buds solitary, large, subrotund, 2.5 cm wide, 2 cm high, present from the basal node up. Branches initially 3, the central one dominant, two side-branches subdominant, and a few slender branches; usually unbranched on the lower culm, except for short rudimentary branches; branching usually intravaginal, occasionally extravaginal in addition on the lower culm; rebranching. Culm-leaves persistent and decaying on the basal and lower culm, deciduous on the mid-culm and upper culm. Culm-leaf sheaths about 20 cm wide at the base, 15–20 cm long, half as long as the internode or a little shorter, thickly papery, brittle, light or yellowish-green and often with streaks when young, light straw-colored when dry, scattered with irregular patches of dark brown appressed hairs; margins dark brown long-ciliate when young, eciliate or nearly so when old; apex horizontally truncate, symmetrical or slightly asymmetrical, 6–8 cm wide. Culm-leaf auricles rim-like, subequal, each about 1–2 cm long, of low height, about 1 mm high where connected with the blade, increasing to 3 mm height towards the rounded ends, reaching the sheath margin, glabrous, without bristles, or with a few inconspicuous very short rudimentary bristles, glossy blackish when young, dull dark straw-colored when dry. Culm-leaf ligule about 1 mm high, entire. Culm-leaf blades papery, persistent or late caducous, initially erect, becoming deflexed, broadly lanceolate (not triangular), the junction with the sheath half as wide as the sheath apex; height a little shorter or a little longer than the sheath on the lower culm, longer on the mid-culm and upper culm; green when young, light straw-colored when dry. Foliage-leaves (7) 12–16 (19) per branchlet. Foliage-leaf sheaths keeled, light green when young, light straw-colored when dry, minutely pale and dark hairy when young, becoming glabrous and smooth soon; margins eciliate. Foliage-leaf auricles small rounded lobes, usually less than 1 mm long and wide, glabrous, dark colored when young, without bristles. Foliage-leaf ligule inconspicuous; outer ligule present. Foliage-leaf blades tough, medium-sized to large, 18–29 (>30) × 2–3.5 (4) cm, lanceolate, glabrous on both surfaces, dull mid-green on both surfaces; base rounded to wedge-shaped; apex attenuate; margins antrorsely scabrous; midrib proximally prominent on both surfaces, yellowish green beneath; pseudopetiole 3–7 mm long.

Uses: Not recorded; plants suitable for landscaping.

Comments:

(1) No record was found on the origin of the Australian plant; perhaps it derived from seeds or was collected from Bali, Indonesia.

(2) Provisional identification: Gigantochloa sp.; BS-0507 is most similar to Gigantochloa ridleyi, but they are different species. In Gigantochloa ridleyi, internodes are longer, the culm-leaf sheath is covered with black (not dark brown) hairs, the sheath apex is obtuse-triangular truncate, the auricles (of both, culm-leaf and foliage-leaf) do not reach the sheath margin, the culm-leaf blade is broad triangular (not lanceolate), foliage-leaves are less numerous per branchlet, foliage-leaf blades are glossy dark green, longer and broader.

(3) It was assumed that BS-0507 represents Gigantochloa aya. However, Gigantochloa aya was described as having scattered white hairs on the lower leaf blade surface, and culm-leaves with a triangular blade. Both features could not be found in BS-0507.