The orchid family consists of a large number of genera, each with its own unique characteristics. A common characteristic, however, is the basic form of the flower, which consists of three petals surrounded by three sepals—often in dramatic and contrasting colors and in a variety of shapes and sizes. Although some orchids are native to temperate zones, most orchids tend to prefer a semitropical or tropical environment (USDA Zones 9 to 11) and have epiphytic roots—meaning they derive moisture and nutrients from the air and support from another plant; few orchids grow in soil. Orchids usually prefer a diurnal temperature fluctuation—meaning warmer days and cooler nights—though the absolute temperature range (cool, intermediate, or warm) varies by genus and is consistent with their natural habitat. While requiring adequate sunlight for a stunning bloom display, most orchids will not tolerate sustained direct sun.