Although vegetatively similar to Ornithogalum thyrsoides in its small bulb with pale, membranous tunics and slender, suberect leaves clasping the stem at the base, O. ceresianum is distinguished by the large, dark olive central eye that covers the basal third of the tepals, the glossy black ovary, and by having all six filaments expanded and winged in the lower two thirds. The inner filaments are more broadly winged than the outer and in some individuals may be petaloid with a dark base. In O. thyrsoides the outer filaments are at most slightly expanded, the dark centre of the flower is much smaller, covering no more than the base of the tepals, and the ovary is ovoid and matt. In addition the racemes are typically longer, with the lower pedicels shorter in fruit.
Like O. thyrsoides but with large, dark centre and all filaments ±winged.
Plants 200-350 mm high. Bulb subglobose, (11-)13-20 mm diam., outer tunics whitish, sometimes brownish grey, somewhat leathery or membranous. Leaves 3-7, suberect, more than half as long as inflorescence, sometimes reaching to base of raceme, partially or mostly dry at flowering, oblong-lanceolate, 40-90(120)x 7-14(-18) mm, attenuate, clasping stem in lower part, glabrous. Raceme subcorymbose to conical, compact, 30-80 mm long at flowering, elongating to 60-100 mm long in fruit, 7-15(-20)-flowered, sometimes two per bulb; lowermost pedicels 27-37 mm long, elongating to 30-40 mm in fruit; bracts pale brownish and papery, ovate, acute or acuminate, lowermost 20-26 mm long, shorter than lowermost pedicels. Flowers creamy white with large, dark olive green central stain covering basal third of tepals, outer tepals ovate-lanceolate, inner obovate lanceolate, 16-21 x 7-11 mm. Stamens half as long as tepals; filaments 7-9 mm long, white, expanded and winged in lower two thirds, outer with shorter narrow wings, inner with longer wings. Ovary obovoid, 4-6 mm long, truncate, 3-lobed, glossy dark green to black in upper half, greyish below; style erect, 3.0-3.5 mm long, black. Capsule oblong-ellipsoid, 3-lobed, 10-12 mm long. Seeds angular-tetrahedral, 1.5-2.0 mm long, rugulose.
Vleis and moist flats.
Loamy soils in seasonally moist vleis and along seasonal streams, usually in dense colonies.
A local endemic of the Warm Bokkeveld around the town of Ceres.