Orchids comprise one of the largest families found in the plant kingdom with more than 35,000 recognized botanical species. Orchids are found throughout the world, except for Antarctica. Most orchid species grow in tropical forests, but others can be found in semi-desert regions, near the seashore and in the tundra. Their size varies from five millimeters to five meters.
Orchids which have a monopodial growth habit do not have rhizomes or pseudobulbs. They grow continually upward from the crown of the plant. The stem has a strong apical dominance, which insures that flower inflorescences will appear in the axils of the leaves, and not in the crown of the plant (terminal inflorescence). Some members of this group, such as the genus Vanda, will produce aerial roots along their long stems, allowing for stem “cuttings”. Others in this group (i.e. Phalaenopsis, etc), which produce little or no kiekis (baby plants), reproduction from seed or cloning in the laboratory is the only option to reproduce them.
Orchids which have a sympodial growth habit have a lateral growth pattern in which each new growth arises from the apical renewal bud or eye, found at the base of the last growth. The flower spikes will emerge from the tops of these new growths (i.e. Cattleya), or at the base of them (i.e. Cymbidium). Over time, these plants can grow to be a substantial size. The plants can then be divided by separating the rhizomes into groups of at least three to ensure a positive outcome.
Source: Espace pour la vie, Montréal
In many sympodials, there is a swelling at the base of the stem which is called a pseudobulb. It serves as a storage organ by accumulating water and food in anticipation of rest periods. The shape of the pseudobulb varies according to genera and species, from ovoid to elongated.
Orchids are, for the most part, epiphytes (grow on branches and tree trunks), lithophytes (grow on rocks) or terrestrial and semi-terrestrial (grow in peat bogs). They are not parasitic plants: their roots have adapted to attach themselves to tree branches and trunks. In the case of epiphytes, they attach themselves in places where they can receive the optimal amount of light and other resources to grow in optimal conditions.
Most orchids flower once a year, and the duration of the bloom varies between species and hybrids. The initiation of flower spikes is linked to one or more factors (light intensity, temperature, as well as the photoperiod).
Flowers use the most ingenious ways to lure their pollinators: by imitation, chemical or visual seduction, or by provocation. Orchid flowers are composed of three sepals and three petals, one of which is modified into a lip. This is often curled and colored to attract pollinators to the stamens and pistil, which are fused into an organ called a column. The column is a unique feature of orchids.