Oncidium orchids have three petals, one of which is highly modified and also called lip or labellum. This modified petal is always in a lower position in comparison to the others. It is often bigger or show more attractive colors, providing a type of porch for many pollinating insects, such as bees and butterflies. In Oncidium ampliatum, both petals and lip are bright yellow, but the lip is much bigger than the petals. Oncidium crispum is a species from Brazil with coppery red to greenish-brown large ruffled petals, which are almost as big as the lip.
In most flowers, sepals are small and green, and are found at the base of the petals. In orchids, sepals are modified outer segments and look very similar to petals. Oncidium orchids have three sepals, which come in a variety of color patterns, shapes and sizes, according to the species. In Oncidium hastilabium sepals are cream with mahogany lines.
The column is a tubular structure located at the center of the Oncidium orchid, where the reproductive parts are found. The masculine organs or pollinia, a waxy mass of grains of pollen, are found at the top of the column. The stigma or female reproductive organs are found at the bottom of the column. The stigma is covered in a sticky substance, which helps to increase pollen adherence.
Oncidium orchids have roots with pseudobulbs, which are structures designed to store water. Oncidium orchids often have stiff and erect leaves, which vary in size and shape, according to species. In Oncidium ampliatum, leaves are about 15 inches long and 5 inches wide, while Oncidium carthagenense has leaves that reach up to 24 inches in length, and show diminutive reddish spots during growing season.