Appearance and Orchids Structure

Orchids, like the grasses and the palms, which they resemble in some ways—for instance the form of their leaves—are monocotyledons. They have one cotyledon, or embryonic leaf, in contrast to the two of most flowering plants.
Orchids are cosmopolitan in distribution, occurring in every habitat, except Antarctica and deserts. The great majority are to be found in the tropics, mostly Asia, South America and Central America. They are found above the Arctic Circle, in southern Patagonia and even on Macquarie Island, close to Antarctica.

Longitudinal view of a vanilla flower, showing the column.

The following list gives a rough overview of their distribution:
•Eurasia: 40–60 genera
•North America: 20–30 genera
•tropical America: 300–350 genera
•tropical Africa: 125–150 genera
•tropical Asia: 250–300 genera
•Oceania: 50–70 genera
Orchids can be grouped 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, mostly trees, sometimes shrubs. However, they are not parasites.
•A few are lithophytes, similar to epiphytes but growing naturally on rocks or on very rocky soil. They derive their nutrients from the atmosphere, rain water, litter, humus, and even their own dead tissue.
•Others are terrestrial plants. They grow in the soil or in the loose substrate atop the ground and obtain their nutrients from the soil or the substrate. This group includes nearly all temperate orchids.
•Some lack chlorophyll and are myco-heterotrophs (formerly incorrectly called saprophytes). These achlorophyllous orchids have an ectomycorrhizal relationship, i.e. they are completely dependent on soil fungi feeding on decaying plant matter (usually fallen leaves) to provide them with nutrients. Typical examples include the Bird's-nest Orchid (Neottia nidus-avis) and Spotted Coral-root (Corallorrhiza maculata).
Most advanced orchids have these five basic features:
•The presence of a column, also called gynostemium
•The flower is bilaterally symmetric (zygomorphic)
•The pollen are glued together into the pollinia, a mass of waxy pollen on filaments.
•The seeds are microscopically small, lacking endosperm (food reserves) in the overall majority of the species. There are notable exceptions, such as Disa cardinalis, whose seeds may grow to a length of 1.1 mm. Seeds of Vanilla may weigh 20 times or more than that of other orchids.
•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. Germinating seeds in agar, usually done in flasks, is an advanced technique, requiring sterility at all costs. It takes anywhere from one–up to five to ten years for an orchid seedling to mature. An alternative type artificial germination, however, is done by cultivating the fungus and sowing the seeds on them. This is called in-vitro symbiotic culture and is used most commonly for terrestrial orchids.