Many are native to higher elevations in the tropics and grow best at cool temperatures year round. There are both terrestrial and epiphytic types. Seeds of orchids are extremely small, about the size of particle of dust. The vanilla orchid is the original source of natural vanilla. Epiphytic orchids are divided into two groups, sympodial and monopodial, based on their stem structure.
Monopodial orchids grow upright and develop side shoots, which also grow upright.
They bear their leaves in two ranks, perpendicular to the stem and do not produce pseudobulbs. Sympodial orchids often have pseudobulbs, a thickened stem from which the leaves arise. Their growth is horizontal, the pseudobulbs being attached to a common basal rhizome. Growth of the pseudobulbs and extension of the rhizomes develops out of the base of the old pseudobulbs. These pseudobulbs store food and water and enable the orchid plant to withstand periods of drought.