Orchids make up the largest family of flowering plants. To date, more than 30,000 species of orchids in some 750 genera have been identified. These plants are found everywhere on the planet, except in polar and desert regions. New species are still being discovered, even today. Their tremendous variety and spectacular blooms make orchid growing a hugely popular activity around the world.
Plants in the Orchidaceae family are identified on the basis of their unique flower structure. They all have three sepals and three petals, one of which is modified into a labellum*, which plays a major role in attracting pollinators. In addition, instead of having a pistil and stamens, they have a column that bears the male and female parts of the flower.
Orchids can be broadly divided into three growth habits. It is important to know to which group a plant belongs, because they each have different requirements.
- Terrestrial orchids grow on the ground, with their roots in the topmost layer of humus. Most orchids in this category are from temperate regions. Although it grows in the tropics, the Paphiopedilum genus belongs in this group.
- Epiphytic orchids grow on other plants, although they are not parasitic. They are mostly native to the tropics. The Phalaenopsis and Cattleya genera belong to this group.
- Lithophytic orchids grow in cracks in rocks. The Laelia genus includes some species with this growth habit.
Orchids may also be classified according to their growth pattern. There are two categories: sympodial and monopodial orchids.
- Sympodial orchids produce new shoots from the base of old ones. They develop pseudobulbs, i.e. thickened parts of their stems for storing water and nutrients. These structures allow the plant to become dormant during periods of drought. The Cymbidium and Cattleya genera belong to this category.
- Monopodial orchids continue to grow each year from existing stems. They do not produce any pseudobulbs. Monopodial orchids do not have such a marked dormancy period as sympodial ones. The Phalaenopsis and Vanda genera are included in this category.
* The labellum, or lip, is a highly complex flower part with appendices of all kinds and that comes in a wide variety of shapes. It may be a pseudo-female (Ophrys sp.), landing stage, trap (Paphiopedilum sp.), slide or tunnel (Cattleya sp.). Individual species that use these artifices each attract a specific type of insect. Orchids have also developed a wide variety of fragrances, some subtle and some distinctly unpleasant, to attract their main pollinators, insects and birds.