Oncidium-- (Swartz 1800) is a genus that contains about 330 species of orchids from the    subfamily Epidendroideae of the orchid family (Orchidaceae). This is a complex, difficult genus, with many species being reclassified. Calls are made for splitting this genus into multiple genera. This genus was first described by Olof Swartz in 1800 with the orchid Oncidium altissimum, which has become the type species. Its name is derived from the Greek word "onkos", meaning "swelling". This refers to the callus at the lower lip. Most species in Oncidium are epiphytes, although some are lithophytes or terrestrials. They are widespread from northern Mexico, the Caribbean, some parts of South Florida to South-America. They usually occur in seasonally dry areas. They can be divided in three categories, according to their growth pattern : 1.) Some have green pseudobulbs and long racemes with small flowers and a dominant lip. They are mostly golden yellow, but some are brown or yellowish-brown. 2.) Another group has extremely small pseudobulbs and stiff, erect, solitary leaves. These cylindrical leaves act as a water reserve. They have long racemes with yellow flowers that seem to fan out at the top. Sizes of these orchids can vary from miniature plants of a couple of centimetres to giants with 30 cm-long leaves and racemes of more than one metre long. 3.) Formerly there was a third group, called the Variegata or equitant oncidiums. They have no pseudobulbs, giving fan-shaped shoots of less than 15 cm, with triangular section leaves. These oval, broad and spongy leaves act as storage organs. Their flowers are most complicated with exquisite colors. The sepals are somewhat fleshy. The petals and the lip are membranaceous. These orchids are now classified as Tolumnea. Oncidium species are characterised by the following properties : 1.) Presence of column wings 2.) Presence of a complicated callus on the lip (this can be used to separate the taxa). 3.) Pseudobulbs with one to three leaves. 4.) Several basal bracts at the base of the pseudobulbs. The flowers of the Oncidium genus come in shades of yellow, red, white and pink. The petals are often ruffled on the edges, as is the lip. The lip is enormous, partially blocking the small petals and sepals. Some Oncidium orchids are very long : Oncidum altissimum and Oncidium baueri can grow to a height of 5 m, while Oncidum sarcodes can reach 3 m. They are known as 'spray orchids' among some florists. They are very varied and are easily hybridised with Odontoglossum. Together with closely related genera as Cochlioda and Miltonia, they form the Odontoglossum-alliance. The best hybrids orginate from Oncicium tigrinum and Oncidium incurvum, when crossed with Odontoglossums.