Perennials

(also perennial plants), herbs and subshrubs that persist through more than two winters. Some perennials live several years, and others 20 to 30 years. Some species have a life-span of 100 years (for example, tau-saghyz). Upon reaching a certain age, perennials may flower and bear fruit every year (polycarpic plants); this contrasts with annuals and biennials (monocarpic plants), which flower and bear fruit only one time. Some perennials retain their leaves year round (evergreens). In unfavorable periods (winter, drought), the leaves and other aboveground organs of most perennials die, and only the underground organs remain alive (rhizomes, tubers, bulbs, and roots). In some perennials the aboveground shoots are partially preserved as well (rosettes, creeping shoots, and the lower parts of erect stems).

Sometimes the division of plants into annuals, biennials, and perennials is conditional. For example, the tropical perennial castor oil plant (Ricinus communis) grows as an annual in moderate climates, and annual bluegrass (Poa annua), which generally grows on plains, develops as a perennial in the mountains. Trees and shrubs are sometimes referred to as perennials.