Colocasia oresbia A.Hay

CATE Araceae, 17 Dec 2011. araceae.e-monocot.org

Habitat

Disturbed, mostly rather open sites on banks and road cuttings.

Distribution

Malesia: endemic to Borneo, Sabah & Sarawak

General Description

Robust solitary or clump-forming herb. Stem condensed, creeping to decumbent to sub erect, clothed in marcescent leaf bases, lacking stolons, to c. 40 cm long, c. 12 cm diam., cut tissues rapidly turning rusty orange on exposure to air. LEAVES several together; blades very broadly ovate-sagittate, to c. 60 x 50 cm, deeply peltate, somewhat glossy greyish green adaxially, paler abaxially, not waxy-glaucous (except in very young plants), wettable – not water-repellent; anterior lobe c. 2/3 the length of the blade, widest at the base; primary lateral veins slightly raised adaxially and abaxially, 5–6 on each side of the anterior costa, diverging at 45–90°, the divergence angle diminishing distally along the anterior costa; secondary venation flush, not forming interprimary collective veins; posterior lobes to 15 cm long, with the margins rather crisped in the sinus, peltate for over half their length, the posterior costae diverging at c. 50°; petiole to 80 cm long, sheathing in the lower c. 1/3–1/2, wings of sheath c. 1.5 cm wide, persistent, + straight (i.e. not recurved or inrolled). INFLORESCENCES produced in both juvenile and adult plants, solitary or paired; peduncles almost completely enclosed in sheath of subtending leaf, when paired the sequence perpendicular to the circumference of the stem with the younger one further out, to 25 cm long, glaucous in the upper part, the second subtended by a bicarinate narrowly ovate prophyll extending to half way up the spathe tube at anthesis. Spathe 12–15 cm long, tube narrowly ovoid, pale glaucous green, 3.5–4 cm long, limb erect, narrowly ovate, 8.5–c. 11 cm long, pale creamy yellow, open only at base, the rest convolute. Spadix sessile, c. 10 cm long; female zone c. 3.5 x 1 cm, slightly tapering distally; pistils very numerous (c. 150–400), interspersed irregularly in the lower half of and at the apex of the female zone with c. 2.5 mm long upturned ivory staminodes containing 1or 2 vestigial thecae; ovaries incompletely 3–5-locular (briefly septate at apex only) with parietal placentas and numerous sub-orthotropous ovules; style distinct but very short, less than 0.5 mm long; stigma whitish, minutely lobed, c. 0.5 mm diam.; sterile interstice c. 2 cm long, basally of staminodes distally merging with a constricted zone of much reduced elongate ivory synandrodes; male zone c. 2 cm long x 0.5 cm, synandria ivory, irregularly rhombo-hexagonal c. 1 mm diam (after dehiscence), 2–4-staminate; appendix constricted at base, c. 3 cm long x 0.4 cm, tapering to a point, surface slightly and irregularly rugose. Fruiting peduncle elongating c. 1.5 times, straight, erect to horizontal depending on condition of subtending leaf but not actively down-curved; fruiting spadix aligned with peduncle, c. 10 x 4 cm, enclosed within the expanded spathe tube which dehisces from the base; fruits numbering hundreds per infructescence, green tinged brown when ripe, irregularly subglobose, containing many ovoid, longitudinally ridged, orthotropous, ivory seeds c. 0.75 mm long in clear thin mucilage.