Oncidium.
Family Orchidaceae > Subfamily Epidendroideae > Tribe Cymbidieae > Subtribe Oncidiinae.
Sub-tribe Oncidiinae has about 70 closely related genera with over 1,000 species collectively known as the Oncidium Alliance.
There are hundreds of thousands of hybrids between species in a genus and intergeneric hybrids with up to 5 parent species from the Alliance.
Oncidium, Ondontoglossum and Miltonia are commonly hybridised but many other genera are used.
Oncidium is the largest genus in the Alliance with up to about 650 highly variable species.
Most are epiphytes with some growing on rocks or on the ground.
Size varies from miniatures up to 5 metres tall.
Most have stems reduced to thick ovoid pseudobulbs that may have bracts at the base.
Bracts can be leaf-like or dry and papery.
Each pseudobulb typically has 1 to 3 leaves that can be flat and strap-like or round or triangular in cross section.
Inflorescences can arise from a pseudobulb or, where these are absent from the leaf axils.
The up to around 1 m long stems can be erect, arching or pendulous.
There may be a single flower, a spike or a branched cluster (panicle) with hundreds of flowers.
From 10 cm to 4 m long they have a narrow bract at the base of the peduncles.
Spikes and side branches are racemes with the lower flowers opening first.
Flowers are often a bright yellow with brown, reddish-brown or purplish markings.
Other colours seen include pink, green, purple or white.
The small to large flowers are upside-down (resupinate).
There is one posterior (dorsal or upper) and 2 lateral petal-like sepals.
There are 2 upper petals and a larger lower lip or labellum.
The lip usually has 3 lobes – a narrow base, a middle lobe often with wings and a transversely enlarged terminal lobe.
There is a often a raised callus on the base.
The column of fused stamen filaments and the style has 1 to 3 pollinia under the anther cap at the top.
Below this is the large depressed stigma and separating the two is the beak-like rostellum.
The rostellum has a sticky viscidium disc on the tip.
The inferior ovary has 1 locule with numerous ovules.
The fruit are a capsule.
J.F.
