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.