Some Oncidium species are pollinated by Centris bees, which may visit the flowers to collect floral oils. However, for many Oncidium species it is doubtful there is sufficient oil present to function as anything other than an attractant, in which case this would be an example of deceit pollination. (Pridgeon 2009) Powell (2008, cited in Chase et al. 2009) found that the yellow-flowered species with typical Oncidium morphology have floral UV-absorption patterns that mimic those of similarly colored species of Malpighiaceae. These malpighs have sepalar glands that produce oil collected by female Centris bees as food for their larvae. No other yellow flowers have been shown to have this same pattern of light absorbance. Thus, there may be a continuum of Oncidium species ranging from those that mimic malpigh flowers in color but offer no reward to some that actually produce enough oil to reward a pollinator. The flowers of some Oncidium species are autogamous (self-fertilizing). (Cingel 2001; Powell 2008)
Some male Centris use Oncidium flower clusters as the focal point for their territories, which they defend against other flying insects. These males reportedly attack Oncidium flowers moving in the wind as if they were trespassing insects, striking them very precisely and receiving a pollen load in the face. (Cingel 2001 and references therein)
The Neotropical orchid genus Oncidium includes more than 400 known species, at least in its broadest definition. However, the limits of the genus have been a matter of controversy for many years. Chase and Palmer (1992, cited in Chase et al. 2009) first showed that Oncidium as commonly circumscribed was polyphyletic (i.e., the traits traditionally used to place species as members of this genus are shared because they evolved several times independently, not because of shared ancestry). Subsequent studies have confirmed and extended this early work and progress has been made in redefining genera--splitting some species out of Oncidium and merging others--to make Oncidium monophyletic (a monophyletic group being one that includes all [and only] the descendant species of a single common ancestor). (Chase et al. 2009 and references therein)
Oncidium orchids are mainly epiphytic. They are found from Mexico and southern Florida (U.S.A.) through Central America and the Caribbean to Brazil, Bolivia, and Peru. The two centers of diversity are in Mexico and the Andes (according to the recent analysis by Chase et al. [2009], just a single species is known from Brazil). Various species occur from near sea level up to around 2500 meters in elevation, in both exposed situations and dense shade.
It appears that Oncidium as a genus has historically been defined by flower characteristics directly related to its pollination biology (pollination by Centris and possibly other bees). Chase et al. (2009) note that it is unsurprising that natural selection should have resulted in some convergence in these floral traits among several independent lineages, making Oncidium (as traditionally defined) polyphyletic. They advocate minimizing reliance on floral characters in circumscribing genera within the Oncidiinae (the group including Oncidium and related genera) and instead focusing on chromosome number and vegetative characters, such as the structure of pseudobulbs.
Oncidium orchids are widely cultivated for the cut flower trade. The confusing historical taxonomic treatment of this group, combined with very extensive hybridizing by breeders, makes identification of Oncidium species and varieties very challenging, With this in mind, Wu et al. (2010) sequenced the chloroplast genome of a cultivated Oncidium and explored chloroplast sequence variation in a number of other Oncidium varieties. They concluded that, although additional data from the nuclear genome are clearly desirable, data from the chloroplast genome hold great promise for phylogenetic and evolutionary studies in Oncidium breeding and variety identification.
Oncidium, abbreviated as Onc. in the horticultural trade,[2] 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.[1][3] Common names for plants in this genus include dancing-lady orchid[4] and golden shower orchid.
In 2008, Oxfords Annals of Botany labeled the Oncidium alliance "grossly polyphyletic."[5] The American Orchid Society labeled this genus a "dumping ground."[6] After DNA testing and much debate, a consensus was announced (April 2013)[7] 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.[8] 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.[6][5] The Royal Horticultural Society system, the World Checklist of Monocots database[9] and the American Orchid Society have already updated their databases to reflect most of these changes.
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 (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.
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.
