Flora of Barro Colorado Island

Dioscorea macrostachya

Benth., Pl. Hartweg. 73.1839

Dioecious twining vine, glabrous; stems twisting to the right. Leaves alternate; petioles slender, 2-7 cm long; blades ovate-cordate, narrowly acuminate, with a broad or narrow sinus at base, 4-12 cm long,     2-9.5 cm wide, usually obscurely pellucid-lineate, with a few, scattered, rounded, crateriform, whitish glands on lower surface especially in axils of veins; veins usually 9, palmate. Flowers unisexual; staminate inflorescences usually soli­tary in leaf axils, 4-12 (30) cm long, simple or branched; flowers solitary, borne on short-stalked fascicles, usually with a single open flower and 1 or more buds; peduncles 0.5-3 mm long, usually with a slender bract about mid­way; perianth segments violet-purple except sometimes greenish on margins, broadly ovate, to 1 mm long, spread­ing at anthesis; stamens 6, all fertile, borne on the hypan­thium at the center of the flower; anthers about as broad as long, dehiscing extrorsely or upward; filaments stout, shorter than the width of the anther; pistillode stout, slightly exceeding stamens. Pistillate inflorescences usu­ally solitary and unbranched, commonly somewhat longer than staminate ones, usually to 20 cm long; pistillate flowers solitary, ± sessile, to 5 mm long at anthesis, bearing 1 or 2 lanceolate bracts at base; perianth lobes as in staminate flowers; staminodia lacking; styles 3, short and stout, each with a pair of short, divergent branches; ovary sharply 3-angled, soon curved upward along the pendent rachis. Capsules 3-winged, 2-3 cm long, tan, smooth, the valves obovate to broadly oblong, truncate to emarginate at apex, abruptly tapered and short-stipitate at base; seeds flat, ± oblong, 8-12 mm long, 5-8 mm wide, winged all around, brown, one side usually straight, the seminiferous area to 5 mm long and 3.5 mm wide. Shattuck 680.

Apparently rare on the island, though moderately common in surrounding areas of the Canal Zone. Flowers throughout most of the year, especially in the very late rainy season and in the dry season (November to March). The species may flower twice per year, since there seems to be a second burst of flowering in the early rainy season. Most fruits probably mature during the late dry and early rainy seasons.

Although Standley reported D. macrostachya, the specimen he cited (Shattuck 582) was                   D. polygonoides. Mexico to Panama. In Panama, known principally from tropical moist, premontane wet, and tropical wet forests on the Atlantic slope, but also from premontane wet forest at higher elevations on the Pacific slope in Panama and from tropical moist forest in Veraguas and Darién; apparently rare in premontane moist forest in the Canal Zone on the Pacific slope.