The Odontoglossum Alliance is a huge group of orchids, at the centre of which is the genus Odontoglossum. These plants will readily interbreed with many other closely related genera, producing some of the most complex hybrids in the orchid kingdom. Sometimes up to seven or eight different genera have been involved in producing a hybrid unlike any naturally occurring species. Oncidiums and miltonias are some of the plants most readily hybridized, but these are classified under their own heading as they produce many fascinating hybrids within their own groups.

Odontoglossums and their related genera are widespread throughout Central and South America. They are mostly high-altitude plants, requiring cool conditions, from the Andes, crossing the Panama isthmus and as far north as Mexico. Recent taxonomic changes within these closely related plants have resulted in many of the families being split up, with the creation of new genera. For example, all the former odontoglossums that came from Guatemala and Mexico have now been regrouped as Lemboglossum, Rossioglossum and so on, leaving only the plants found in the Andes, mosdy from Colombia and Ecuador, in the genus Odontoglossum.

The area from which these orchids originate is cool cloud forest which, although dose to the equator, is never too hot during the day and always cool at night. These orchids are, therefore, difficult to grow in tropical countries. In Britain, the Victorian growers fell in love with the odontoglossums and called them the queen of orchids. At one time they were being imported at a rate of 100,000 plants each year, many of which perished on the long sea journey from South America, or failed through lack of understanding in overheated Victorian greenhouses.

O. crispum fascinated them the most as it came in several hundred different varieties, from pure white to heavily spotted yellow and maroon flowers. Because of the inaccessibility of the high valleys in which these orchids grew, each variety had evolved separately in its own isolated environment.

As well as O. crispum, O. pescatorei, O. hallii and O. triumphans were among the orchids that were available in unlimited quantities at the turn of the century. The over-collecting of these plants led to their near extinction in the wild and, sadly, very few of them are to be found in cultivation today.

The Hybrids
The greatest demand is for Odontoglossum hybrids that have been crossed with related genera such as Miltonia, Oncidium and Cochlioda, which not only increase the range of colour, shape and size but give a more vigorous plant. When two genera, such as Odontoglossum and Cochlioda, are crossed together, the two names are used to produce the name for the new plants; in this case, the resulting hybrids are called Odontioda. When such a hybrid is crossed with another genus, for example Miltonia, the new plants are named after the breeder, in this case Vuylstekeara, named after Charles Vuylsteke. All intergeneric hybrids arising from three or more natural genera are named after a person in this way.

The introduction of Brassia or Oncidium into the blood of such hybrids will make the resulting plants more heat tolerant, which means that some of them can be grown in Florida and other places that would normally be too warm for the pure odontoglossums.

Cultivation and Care
A strong, healthy, mature plant should consist of four to six pseudobulbs each with a strong new growth. These orchids do not make enormous specimen plants and will seldom grow at the same time as they flower. Each pseudobulb consists of two basal leaves and one or two terminal leaves from the top, the flower spike coming from the base or side of the pseudobulb.

Due to their origins, living in almost perpetual spring-like weather, these orchids know little or no seasonal change and therefore grow continuously without a definite flowering season. In fact, most of these plants will grow and flower on a nine-month cycle, so they seldom bloom at the same time two years running, with the result that a mixed collection of the Odontoglossum Alliance will give flowers almost all the year round.

These orchids are best grown in a cool greenhouse with a minimum night-time temperature of 10 °C (50 °F), with a variable daytime rise depending on the weather. From early spring onwards, the greenhouse should be well shaded to prevent overheating and scorching of the foliage, especially on hot summer days. The floor and staging should be kept constantly moist to provide an even humidity; combine this with fresh air to give a buoyant atmosphere.