Oncidium is a large genus of plants within the Orchidaceae family that has over 500 species. These orchids can be identified by their bright bursts of numerous flowers that have colorful swollen bottom petals. Members of this genus can be found growing in regions varying from sea level to mountain elevations in excess of 4,000 miles (about 6,500 km). Most Oncidium orchids grow in the soil, but there are also species that are epiphytes, meaning they are able to survive without soil.
The densely arranged flowers of Oncidium blossoms are often categorized as spray orchids. An Oncidium, referred as Onc. by horticulturalists, has sprays of flowers that blossom at the same time and lack spurs, or tubes that lead to nectar. The arrangement of these cheerful sprays of flowers is sometimes called a 'dancing lady' pattern by orchid enthusiasts. The vast majority of the orchids in this genus have yellow or yellow-brown flowers, but there are also Oncidiums with flowers that are green, red, or pink.
Most Oncidiums require plenty of bright, direct sunlight in order to thrive. Larger species should be planted in a hanging basket with abundant tree ferns, while smaller species should be planted in a flower pot with well-draining soil. Some Oncidiums are sprawling plants that will need to be repotted periodically. During the growing season, all Oncidium orchids need to be watered and fertilized regularly.
Many orchid enthusiasts prefer to mount their Oncidiums on cork trees and other natural structures that mimic the plant's natural environment. Each Oncidium produces a cluster of flowers once a year if the plant is properly cared for. Oncidiums bloom during the summer with long-lasting flowers.
The sheer volume of species contained in the Oncidium genus has prompted botanists to organize these orchids into four informal categories. These categories are determined by the plant's foliage and include fan-shaped species, thin-leaved species, thick-leaved species and pencil-leaved species. Some experts have suggested that the entire Oncidium genus should be permanently split into these categories for the sake of clarity.
Fan-shaped Oncidiums like O. pulchellum and O. urophyllum have small fans of overlapping leaves that are similar to an iris's foliage. Thin-leaved Oncidiums such as O. maculatum and O. crispum grow with clusters of pseudobulbs, or false bulbs, that produce multiple pairs of thin leaves. Thick-leaved Oncidiums like the O. carthagenense are native to North America and have large, thick leaves that resemble horse's ears. Pencil-leaved Oncidiums have long, narrow leaves and are epiphytes.