Research and Conservation in Southern Sonora, Mexico

Oncidium cebolleta (orquídea, rattail orchid)

Cebolleta means little scallions (green onions), which the plants resemble. This is probably one of its common names somewhere in its large range, but it is not used in Sonora. Pencil-thick or thicker, rigid, terete, succulent leaves less than a foot long arise from tiny pseudobulbs on a creeping rhizome. In late winter branched inflorescences one to three feet long bear numerous bright yellow flowers less than an inch across. Widespread in southern Sonora but never common.

Plants of Oncidium cebolleta growing on Vitex mollis, road to Guajaray, Sonora. Photos: Mark Dimmitt

Description: Rhizomes short, the pseudobulbs cylindrical, inconspicuous, 11-19 mm long. Leaves evergreen, single, 6-27.5 cm long, ca. 5-10 mm wide, semisucculent, linear-subulate terete with a broad, shallow dorsal groove, green to often reddish green and with dark reddish spots.  

Flowering stems 22-150 cm long, appearing from the base of the leaf blade, the inflorescences racemose to paniculate. Flowers yellow with red-brown markings, 16-29 mm long, 15-20.5 mm wide. Pedicellate ovary 24.5-30 mm long. Sepals and petals obovate, clawed, 10.3-14 mm long, somewhat ruffled, pale yellow with reddish brown spots, blotches and mottling, the apices acute. Lip petal 15.8 [--] mm long, bright yellow above, pale yellow mottled with pale reddish blotches below, the middle lobe reniform, 12.7 [--] mm wide, the lateral lobes more or less broadly elliptic. Callus with a thick ridge-crest and irregular protuberances, yellow to whitish with pale reddish blotches. Column thick, 4.5-4.7 mm long, bright yellow with reddish markings, with 2 large, thick lobes the lip side, and 2 small ear-like lobes above; rostellum 2.6-3.0 mm long, short-papillate, yellow with some reddish papillae as dots, spots, or margins. Anther 1.4-1.5 mm long, more or less cuneate, transparently colorless to brownish at very base, the sticky foot yellow-orange to brownish; pollinia bright yellow, 0.9-1.1 mm long. March and May; fruits in early summer.

Flowers of Sonoran Oncidium cebolleta in cultivation. Photo: Mark Dimmitt

Oncidium cebolleta growing on a rock cliff in southern Sinaloa. Photo: Albert van der Heiden

Riparian canyons and sometimes on mountain slopes; tropical deciduous forest and oak forest; 350-920 m. SE and EC Sonora and SW Chihuahua to South America and West Indies.

Plant of Sonoran Oncidium cebolleta in cultivation. Photo: Mark Dimmitt

Often on sheer canyon walls and cliffs, and large rocks, usually with north-facing exposures or shaded. Also common as an epiphyte, and mostly on the undersides of limbs, on both living branches and dead limbs. The northernmost population occurs in the Río Yaqui drainage, between Onavas and Tepoca. Here it commonly grows on Vitex mollis in riparian habitats within tropical deciduous forest near the lower limit of oaks. Also seen Fouquieria macdougalii, Guazuma ulmifolia, oaks including Quercus chihuahuensis, Sapindus saponaria, Taxodium mucronatum. This is the most common, wide-ranging, and xerophytic epiphytic/lithophytic orchid in northwestern Mexico. The range extends well into South America and the Caribbean islands.

This species is very easy in cultivation, and can even be grown outdoors in Tucson, AZ if protected from frost. Greenhouse-grown plants can become much larger than wild ones.