The term Alliance is used to describe a group of genera that have many common characteristics and can be used for cross breeding. The result of these cross breedings are considered to be a new hybrid genera. Examples of alliances are:
Cattleya Alliance: includes Cattleya, Laelia, Epidendrum, Encyclia, Sophronitis Broughtonia, Rhyncholaelia, Brassavola and all its intergeneric hybrids.
Vanda Alliance: includes Phalaenopsis, Aerides, Ascocentrum, Euanthe, Neofinetia, Rhychostylis, Sarcochilus, Vanda and all its intergeneric hybrids.
Dendrobium Alliance: includes 4 genera, only one of which Dendrobium is widely grown.
Oncidium Alliance: includes Brassia, Cochlioda, Cuitlauzina, Lemboglossum, Miltonia, Odontoglossum, Oncidium, Osmoglossum, Psychopsis, Psygmorchis, Rodriguezia, Rossioglossum, Trichocentrum, Trichopilla, Tolumnia and all its intergeneric hybrids.
Cymbidiums: includes only the Cymbidiums.
Slipper Orchids: includes Crypipedium, Paphiopedilum, Phragmipedium and Selnipedium.