<P> The largest organisms found on Earth can be determined according to various aspects of an organism's size, such as: mass, volume, area, length, height, or even genome size . Some organisms group together to form a superorganism (such as ants or bees), but such are not classed as single large organisms . The Great Barrier Reef is the world's largest structure composed of living entities, stretching 2,000 km (1,200 mi), but contains many organisms of many types of species . </P> <P> This article lists the largest species for various types of organisms, and mostly considers extant species . The organism sizes listed are frequently considered "outsized" and are not in the normal size range for the respective group . </P> <P> If considered singular entities, the largest organisms are clonal colonies which can spread over large areas . Pando, a clonal colony of the aspen tree, is widely considered to be the largest such organism by mass . Even if such colonies are excluded, trees retain their dominance of this listing, with the giant sequoia being the most massive tree . In 2006 a huge clonal colony of Posidonia oceanica was discovered south of the island of Ibiza . At 8 kilometres (5.0 mi) across, and estimated at around 100,000 years old, it may be one of the largest and oldest clonal colonies on Earth . </P> <P> Among animals, the largest species are all marine mammals, specifically whales . The blue whale is believed to be the largest animal to have ever lived . The largest land animal classification is also dominated by mammals, with the African bush elephant being the most massive of these . </P>

What is the largest living organism in the world