Oncidium

Oncidium, abbreviated as Onc. in the horticultural trade, is a genus that contains about 330 species of orchids from the subtribe Oncidiinae of the orchid family (Orchidaceae). As presently conceived (May 2014), it is distributed across much of South America, Central America, Mexico and the West Indies, with one species "(O. ensatum)" extending into Florida. Common names for plants in this genus include dancing-lady orchid and golden shower orchid.
In 2008, Oxfords Annals of Botany labeled the "Oncidium" alliance "grossly polyphyletic." The American Orchid Society labeled this genus a "dumping ground." After DNA testing and much debate, a consensus was announced (April 2013) resulting in major taxonomic changes to "Oncidium, Gomesa, Odontoglossum, Miltonia," and others. Much of this debate and subsequent housekeeping was initiated by significant research for the scientific publication Genera Orchidacearum Volume 5. As a result, much of the information in this article is now deprecated, but still of great value. One significant change is the move of most Brazilian "Oncidium" with a fused lateral sepal to the genus "Gomesa". The Royal Horticultural Society system, the World Checklist of Monocots database and the American Orchid Society have already updated their databases to reflect most of these changes. 
Description.
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 ὀγκος, "onkos", meaning "swelling". This refers to the callus at the lower lip.
Most species in the genus are epiphytes (growing on other plants), although some are lithophytes (growing on rocks) or terrestrials (growing in soil). They are widespread from northern Mexico, the Caribbean, and some parts of South Florida to South America. They usually occur in seasonally dry areas.
They can be divided into three categories, according to their growth pattern:
"Oncidium" species are characterised by the following properties :
The flowers 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 other closely related genera ("Cochlioda", "Miltonia", "Cuitlauzina", "Miltoniopsis", "Osmoglossum", "Leochilus", "Comparettia", "Cyrtochilum", "Odontoglossum", "Tolumnia", "Rhynchostele" [formerly "Lemboglossum"], "Psychopsis", etc.) they form the Oncidium alliance. Some of the best Oncidium alliance hybrids originate from "Oncidium tigrinum" and "Oncidium incurvum", when crossed with Odontoglossums, although hybridization possibilities of this group of orchids are endless, and there are literally hundreds of thousands of excellent hybrids in the Oncidium alliance.