A perennial plant or perennial (Latin per, "through", annus, "year") is a plant that lives for more than two years. When used as a noun, this term applies specifically to perennial herbaceous plants, even though woody plants like shrubs and trees are also perennial in their habit.

Perennials, especially small flowering plants, grow and bloom over the spring and summer and then die back every autumn and winter, then return in the spring from their root-stock rather than seeding themselves as an annual plant does. These are known as herbaceous perennials. However, depending on the rigors of local climate, a plant that is a perennial in its native habitat, or in a milder garden, may be treated by a gardener as an annual and planted out every year, from seed, from cuttings or from divisions.

The symbol for a perennial plant, based on Species Plantarum by Linnaeus is, .

Life cycle

Perennial plants can be short-lived (only a few years) or they can be long-lived, as are some woody plants like trees which can live for over 3,000 years. They can vary in height from only a few millimeters to over 100 meters tall. They include a wide assortment of plant groups from ferns and liverworts to the highly diverse flowering plants like Orchids and Grasses.

Plants that flower and fruit only once and then die are termed monocarpic or semelparous. However, most perennials are polycarpic, flowering over many seasons in their lifetime.

Structure

Perennials typically grow structures that allow them to adapt to living from one year to the next. These structures include bulbs, tubers, woody crowns, rhizomes plus others. They might have specialized stems or crowns that allow them to survive periods of dormancy over cold or dry seasons during the year. Annuals produce seeds to continue the species as a new generation while the growing season is suitable, and the seeds survive over the cold or dry period to begin growth when the conditions are again suitable. Many perennials, in contrast, have specialized to survive under extreme environmental conditions: some have adapted to survive hot and dry conditions, or to survive under cold temperatures. Those plants tend to invest a lot of resource into their adaptations and often do not flower and set seed until after a few years of growth. Many perennials produce relatively large seeds, which can have an advantage, with larger seedlings produced after germination that can better compete with other plants or more quickly develop leaves for photosynthesis. Annuals tend to produce many more seeds per plant since they will die at the end of the growing season, while perennials are not under the same pressure to produce large numbers of seeds but can produce seeds over many years.