Orchids grow in all terrestrial ecosystems, except in the North and South Poles, but their greatest diversity is found in the tropics. Terrestrial orchids predominate in temperate habitats, epiphytes in tropical habitats. Orchids may be divided into two fundamental types based on growth habit. Sympodial orchids, such as cattleyas and paphiopedilums, are characterized by individual shoots with limited growth. Creeping stems called rhizomes are made of basal portions of successive shoots.
Buds give rise to new shoots, each developing to maturity and flowering.
Shoots of monopodial orchids, on the other hand, have unlimited growth, each continuing to produce leaves from the stem apex and inflorescences from between the leaves. Vandas and phalaenopsis are monipodial in habit. Brightly colored, the tubular flowers of Masdevallia hirtzii contrast with the limbs on which the plants grow. The Flowers of all orchids are constructed on a certain basic formula. There is an outer whorl of three generally similar segments called sepals.