Orchids may also be classified according to their pattern of growth . 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.
These orchids 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.