These monocotyledonous plants are cosmopolitan in distribution, except Antarctica and deserts. The great majority are to be found in the tropics, mostly Asia, South America and Central America. Orchids can be classified according to the way they retrieve nutrients:
- a majority of species are perennial epiphytes; they are found in tropical moist broadleaf forests or mountains and subtropics. These are anchored on other plants, such as trees, cacti or tree ferns. But they are not parasites.
- others are terrestrial plants, retrieving their nutrients from the soil. This group includes all European orchids.
- a few are lithophytes, growing on rocks, or lack chlorophyll and are saprophytic. These are mycotrophic, i.e. they are completely dependent on their soil fungi for nutrients. A typical example of such a saprophyte is the Bird's-nest Orchid (Neottia nidus-avis).
All orchids have these five basic features :
- the presence of a column
- the flower is bilaterally symmetrical
- the pollen are glued together into the pollinia, a mass of waxy pollen on filaments.
- the seeds are microscopically small, lacking endosperm (food reserves). A notable exception is Disa cardinalis, whose seeds may grow to a length of 1.1 mm
- the seeds can, under natural circumstances, only germinate in symbiosis with specialized fungi. Under artificial circumstances, however, germination is possible "in vitro" on sterile substrates of agar in specialized laboratories.