A perennial plant or simply perennial (Latinper, "through", annus, "year") is a plant that lives for more than two years. The term is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also widely used to distinguish plants with little or no woody growth from trees and shrubs, which are also technically perennials.
Perennials, especially small flowering plants, that grow and bloom over the spring and summer, die back every autumn and winter, and then return in the spring from their root-stock, 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.
There is also a class of evergreen, or non-herbaceous, perennials, including plants like Bergenia which retain a mantle of leaves throughout the year. An intermediate class of plants is known as subshrubs, which retain a vestigial woody structure in winter, e.g. Penstemon. The local climate may dictate whether plants are treated as shrubs or perennials. For instance, in colder temperate climates, many shrubby varieties of Fuchsia are cut to the ground to protect them from winter frosts.
The symbol for a perennial plant, based on Species Plantarum by Linnaeus, is , which is also the astronomical symbol for the planet Jupiter.
The nativeflora of the United States includes about 17,000 species of vascular plants, plus tens of thousands of additional species of other plants and plant-like organisms such as algae, lichens and other fungi, and mosses. About 3,800 additional non-native species of vascular plants are recorded as established outside of cultivation in the U.S., as well as a much smaller number of non-native non-vascular plants and plant relatives. The United States possesses one of the most diverse temperate floras in the world, comparable only to that of China.
Several biogeographic factors contribute to the richness and diversity of the U.S. flora. While most of the United States has a temperateclimate, Alaska has vast arctic areas, the southernmost part of Florida is subtropical to tropical, Hawaii is fully tropical (including high mountains), and alpine summits are present on many western mountains, as well as a few in the Northeast. The U.S. coastline borders three oceans: The Atlantic (and Gulf of Mexico), the Arctic, and the Pacific. Finally, the U.S. shares long borders with Canada and Mexico, and is relatively close to the Bahamas, Cuba and other Caribbean islands, and easternmost Asia.