A perennial plant (or simply a perennial) can be best described as a plant that lives for more than two years. This differentiates them from annuals and bi-annuals which last for one and two years respectively. Thus, year after year, perennials will emerge from their underground roots in spring, growing, flowering and setting seed before dying back to the ground in the autumn (although there are some evergreen perenials). The rootstock or woody-base will persist throughout the winter and the following spring the cycle will begin again (although some less hardy perennials may require protection). This definition can be applied to other plants including trees, bulbs, grasses and ferns but these are commonly excluded from being described as such.
Examples of notable periennal plants in this section include Achillea (Yarrow) and Crocosmia (Tickseed).