This article lists the largest organisms for various types of life and mostly considers extant species, which 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. When considering singular entities, the largest organisms are clonal colonies which can spread over large areas. Pando, a clonal colony of the quaking 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 the seagrass Posidonia oceanica was discovered south of the island of Ibiza. At 8 kilometres (5 mi) across, and estimated at 100,000 years old, it may be one of the largest and oldest clonal colonies on Earth. Among animals, all of the largest species are marine mammals, specifically whales. The blue whale is believed to be the largest animal to have ever lived. The living land animal classification is also dominated by mammals, with the African bush elephant being the largest of these.
Plants
The largest single-stem tree by wood volume and mass is the giant sequoia (Sequoiadendron giganteum), native to California's Sierra Nevada; it typically grows to a height of 70–85 m (230–280 ft) and 5–7 m (16–23 ft) in diameter. The largest organism in the world, according to mass, is the aspen tree whose colonies of clones can grow up to 8 kilometres (5 mi) in size. The largest such colony is Pando, in the Fishlake National Forest in Utah. A form of flowering plant that far exceeds Pando as the largest organism on Earth in area and potentially also mass, is the giant marine plant, Posidonia australis, living in Shark Bay, Australia. Its length is about 180 km (112 mi) and it covers an area of 200 km2 (77 sq mi). It is also among the oldest known clonal plants. Another giant marine plant of the genus Posidonia, Posidonia oceanica discovered in the Mediterranean near the Balearic Islands, Spain may be the oldest living organism in the world, with an estimated age of 100,000 years. The largest individual flower in the world is Rafflesia arnoldii, while the flowering plant with the largest unbranched inflorescence in the world is Amorphophallus titanum. Both are native to Sumatra in Indonesia.
Green algae Green algae are photosynthetic unicellular and multicellular "green plants" that are related to land plants. The thallus of the unicellular mermaid's wineglass, Acetabularia, can grow to several inches (perhaps 0.1 to 0.2 m) in length. The fronds of the similarly unicellular Caulerpa taxifolia can grow up to a foot (0.3 m) long.
Animals
Fungi
The largest living fungus may be a honey fungus of the species Armillaria ostoyae. A mushroom of this type in the Malheur National Forest in the Blue Mountains of eastern Oregon, U.S. was found to be the largest fungal colony in the world, spanning 8.9 km2 (3.4 sq mi) of area and possibly weighing as much as 35,000 tons. This organism is estimated to be 2,400 years old. The fungus was written about in the April 2003 issue of the Canadian Journal of Forest Research. It is not known, however, whether it is a single organism with all parts of the mycelium connected. A spatial genetic analysis estimated that a specimen of Armillaria ostoyae growing over 91 acres (37 ha) in northern Michigan, United States weighs 440 tons (4 × 105 kg). In Armillaria ostoyae, each individual mushroom (the fruiting body, similar to a flower on a plant) has only a 5 cm (2.0 in) stipe, and a pileus up to 12.5 cm (4.9 in) across. There are many other fungi which produce a larger individual size mushroom. The largest known fruiting body of a fungus is a specimen of Phellinus ellipsoideus (formerly Fomitiporia ellipsoidea) found on Hainan Island. The fruiting body masses up to 500 kg (1,100 lb). Until P. ellipsoideus replaced it, the largest known individual fruit body came from Rigidoporus ulmarius. R. ulmarius can grow up to 284 kg (626 lb), 1.66 m (5.4 ft) tall, 1.46 m (4.8 ft) across, and has a circumference of up to 4.9 m (16 ft).
Lichen Umbilicaria mammulata is among the largest lichens in the world. The thallus of U. mammulata is usually 4 to 15 cm (1.6 to 5.9 in) in diameter, but specimens have been known to reach 63-centimetre (2.07 ft) in the Smoky Mountains of Tennessee. The longest lichen is Usnea longissima, which may grow to exceed 20 feet (6.1 m) in length.
Protists
(Note: the group Protista is not used in current taxonomy.)
Amoebozoans Among the organisms that are not multicellular, the largest are the slime molds, such as Physarum polycephalum, some of which can reach a diameter over 30 cm (12 in). These organisms are unicellular, but they are multinucleate.
Euglenozoans Some euglenophytes, such as certain species of Euglena, reach lengths of 400 μm.
Rhizarians The largest species traditionally considered protozoa are giant amoeboids like foraminiferans. One such species, the xenophyophore Syringammina fragilissima, can attain a size of 20 cm (7.9 in).
Alveolates The largest ciliates, such as Spirostomum, can attain a length over 4 mm (0.16 in).
Stramenopiles The largest stramenopiles are giant kelp from the northwestern Pacific. The floating stem of Macrocystis pyrifera can grow to a height of over 45 m (148 ft). Macrocystis also qualifies as the largest brown alga, the largest chromist, and the largest protist generally.
Heliozoa As of 2021, the largest known heliozoan is Berkeleyaesol magnus (formerly Raphidiophrys magna): its axopodial sphere can reach a diameter up to 6350 μm (6.35 mm), with a cell body diameter of 1486 μm, a mucilaginous envelope 540 μm thick, and up to 1892 μm long axopodia.
Bacteria
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