A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to 6 m; some authors set a minimum of 10 cm trunk diameter (30 cm girth). Woody plants that do not meet these definitions by having multiple stems and/or small size, are called shrubs. Compared with most other plants, trees are long-lived, some reaching several thousand years old and growing to up to 115 m (379 ft) high. Trees are an important component of the natural landscape because of their prevention of erosion and the provision of a weather-sheltered ecosystem in and under their foliage. Trees also play an important role in producing oxygen and reducing carbon dioxide in the atmosphere, as well as moderating ground temperatures. They are also elements in landscaping and agriculture, both for their aesthetic appeal and their orchard crops (such as apples). Wood from trees is a building material, as well as a primary energy source in many developing countries. Trees also play a role in many of the world's mythologies (see trees in mythology). As of 2005, there were approximately 400 billion trees on Earth, about 61 per person.
In response to your question. Sequoia sempervirens is the sole living species of the genus Sequoia in the cypress family Cupressaceae (formerly treated in Taxodiaceae). Common names include Coast Redwood and California Redwood (it is one of three species of trees known as redwoods, but "redwood" per se normally refers to this species). It is an evergreen, long-lived, monoecious tree living for up to 2,200 years, and this species includes the tallest trees on Earth, reaching up to 115.5 m (379.1 ft) in height and 8 m (26 ft) diameter at breast height. It is native to coastal California and the southwestern corner of Oregon within the United States. The name "sequoia" is sometimes used as a general term for the subfamily Sequoioideae in which this genus is classified, together with Sequoiadendron (Giant Sequoia) and Metasequoia (Dawn Redwood); as a common name, it usually refers to Sequoiadendron.
