Gigantochloa ridleyi

Synonym: Gigantochloa maxima var. ridleyi (Holttum) Samsuddin in E. G. Lessard & A. Chouinard, Bamboo Res. Asia, 1980: 92.

Thai names: ไผ่ขี้มอด (phai khi mot) (Nakhon Sawan), ไผ่ผาก (phai phak) (Kanchanaburi).

Distribution: THAILAND (Central): Nakhon Sawan Province; (West): Kanchanaburi Province; wild, in high-humidity mountainous regions at 300–1,000 m altitude. — MYANMAR(?). — MALAYSIA: only known in cultivation. — SINGAPORE: only known in cultivation. — INDONESIA: Bali.

Descriptions:

(1) "Culms densely tufted, straight and erect, up to 20 m tall, 7—10 cm in diameter; internodes to 50 cm long, plain green, non-waxy, glabrous; nodes not conspicuously swollen; walls relatively thin, about 0.6 cm thick at mid-culm portion. Branches developing on the upper part of the culms, the primary one dominant, 1—2 subdominant branches from its base. Culm leaves persistent, coriaceous, dark-green, 23—26 cm long by 32—45 cm wide, top truncate to convex, back covered with appressed dark-brown to black hairs; margin black ciliate, blades dark-green to purple-green, broadly triangular, erect or spreading to deflexed, 14—25 cm long by 8—14 cm wide near the base, covered with dark brown hair on both sides in the middle near the base; auricles dark green, continuing from base of the culm-leaf blade, reach edges of the sheath, about 3—4 mm tall by 20 mm long, margins glabrous; ligule irregularly denticulate to subentire, up to 4 mm high. Leaves 8—13 per branchlet; blades 15—35.5 cm long by 2.2—5.3 cm wide, lower surface slightly pubescent, tessellate, bases acute to oblique-attenuate, occasionally rounded, pseudo-petiole 5—10 mm long; leaf sheaths 8—12 cm long, covered with appressed black hairs; auricles dark brown, rounded, glabrous lobes to 1 mm high; scale-like callus present, crescent, glabrous, shining, 1 mm high by 3 mm wide; ligule a low glabrous rim 1—1.5 mm high, margin sub-entire; secondary veins 8—12 pairs, intermediate veins 5—7. … [flowers described, seeds unknown]". — C. Rattamanee, Revis. Gigantochloa in Thailand, 2014: p. 108-112, fig. 38-40 [#1225].

(2) "Culms 16 m. tall by 10 cm. thick, internodes glabrous, green. Culm-sheaths up to 25 cm. long, covered with blackish appressed hairs, persistent; blades erect, triangular, appressed to the culm when young; auricles continuous with the blade, low, with short curved bristles; ligule about 3 mm. high. Leaf-blade up to 40 x 6 cm., glabrous but for a few hairs near the midrib, stalk up to 5 mm. on the lower leaves, up to 1 cm. on the upper leaves, young sheaths hairy, auricles small glabrous, ligule low." — H. B. Gilliland & al., Revised Flora of Malaya, vol. 3, 1971: p. 36 [#1039].

(3) "… Rhizomes short; pachymorph. Culms erect; 1600 cm long; 100 mm diam.; woody. Culm-internodes terete; mid-green; distally glabrous. Lateral branches dendroid. Branch complement several. Culm-sheaths persistent; 25 cm long; hispid; with appressed hairs; with black hairs; auriculate; setose on shoulders. Culm-sheath ligule 3 mm high; entire. Culm-sheath blade triangular; demarcated but persistent; erect; 8–10 cm long; 60 mm wide; pubescent. Leaf-sheaths hirsute. Leaf-sheath oral hairs lacking. Leaf-sheath auricles erect. Ligule an eciliate membrane. Collar with external ligule. Leaf-blade base with a brief petiole-like connection to sheath; petiole 0.4–0.5 cm long. Leaf-blades oblong; 40 cm long; 60 mm wide; chartaceous. Leaf-blade surface glabrous. Leaf-blade apex acuminate …" — Kew GrassBase [#1335].

(4) K. M. Wong, Bamboos of Peninsular Malaysia, 1995: p. 134, fig. 74 [#1210].

(5) E. A. Widjaja, Revis. Malesian Gigantochloa, 1987: p. 347-349, fig. 23 [#1224].

Images: Photos in AsianFlora (habit) [#1332]; BambooWeb.info [#1340].

Specimens: BS-0474 [C7], BS-0474-1 [-] (living plants), Singapore Botanical Gardens, from the type locality, coll. by C. S., received 1 June 2010.

Characteristics: Habit tight caespitose. Rhizome pachymorph, short-necked [n.v.]. Culms straight, erect, slightly bending outwards above, over 15 m tall [ultimate height not yet known]. Young shoots mid-green, with dark green erect culm-leaf blades, with patches of dark hairs; emerge from June to September. Culm-internodes terete, 35–55 cm long, dull dark green, somewhat rough on the upper third, otherwise glabrous and smooth, not farinose, diameter 5 cm [ultimate diameter not yet known]; thick-walled, lacuna diameter of the same size as the wall width on the lower culm. Culm-nodes glabrous, smooth, flat; sheath scar marginally protruding; supranodal line discernible, without a ridge, about 10 mm above the nodal line; aerial roots on the basal nodes present. Branch-buds solitary, large, subrotund, 2.5 cm wide, 1.6 cm high, present from the basal node up. Branches initially 3, central one dominant, two side-branches subdominant, and several smaller unequal branches; usually unbranched on the lower culm; branching intravaginal; rebranching. Culm-leaves persistent and decaying on the basal and lower culm, late deciduous on the mid-culm and upper culm. Culm-leaf sheaths about 25 cm wide at the base, 23 cm long, slightly shorter or longer than half the internode length on the lower culm, half the internode length or a little shorter on the mid-culm and upper culm, leathery, rigid, light green when young, light straw-colored when dry, scattered with irregular patches of black appressed hairs, or initially dark brown hairs changing to black with age; margins black long ciliate when young, eciliate or nearly so when old; apex obtuse triangular truncate, asymmetrical, 9–12 cm wide. Culm-leaf auricles rim-like, each about 2 cm long, of low height (1 mm), increasing to 3 mm height towards the rounded end, not reaching the sheath margin, glabrous, without bristles, glossy dark green when young, dull dark straw-colored when dry. Culm-leaf ligule about 1–3 mm high, entire. Culm-leaf blades papery, persistent or caducous, stiffly erect on the lower culm, deflexed on the mid-culm and upper culm, broadly triangular (not lanceolate), the junction with the sheath about 6 cm wide, half as wide as the sheath apex; height one-third or half as long as the sheath on the lower culm, as long as the sheath on the mid-culm and upper culm; green when young, light straw-colored when dry; covered with short blackish hairs near the blade base in the middle at the junction with the sheath, for a roughly triangular-shaped spot with a width and height of about 4 cm, on both surfaces, abaxially usually thinly covered, adaxially thickly covered. Foliage-leaves 7–10 (11) per branchlet. Foliage-leaf sheaths keeled, light green when young, dark straw-colored when dry, minutely pale hairy when young, becoming glabrous and smooth soon; the apex reddish when young; margins eciliate. Foliage-leaf auricles small rounded lobes, usually less than 1 mm long and wide, not reaching the sheath margin, glabrous, reddish when young, without bristles. Foliage-leaf ligule inconspicuous; outer ligule present. Foliage-leaf blades tough, large, 29–40 (55) × 4–6 (9) cm, lanceolate, glabrous on both surfaces, glossy dark green above, dull dark green beneath; base rounded to wedge-shaped; apex attenuate; margins antrorsely scabrous; midrib proximally prominent on both surfaces, light green beneath; pseudopetiole 5–8 mm long. Flowers and seeds are unknown.

Uses: Plants for landscaping.

Comments:

(1) In the 1990s, flowers and seeds from a single plant "Gigantochloa ridleyi" in Queensland, Australia (which came from Bali), were recorded by Muller (K. M. Wong, 2004: 69). This plant might be a genuine Gigantochloa aya.

(2) Gigantochloa ridleyi was also recorded to occur in cultivation in Bali, Indonesia, under the local names tiying kaas and tiying aya (S. Kartodihardjo). It seems, however, that the Balinese plants were later recognized as a separate species, Gigantochloa aya (E. A. Widjaja & al., 2004: 201).

(3) The type plant of Gigantochloa ridley is still extant in the Singapore Botanic Gardens, but there are no records that it has ever flowered. (J. F. Veldkamp & al., Poaceae (Gramineae), in: Flora of Singapore, Vol. 7, 2019: p. 244 [#1283]).