The fungus Armillaria bulbosa is among the largest and oldest living organisms

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ASEXUALLY reproducing organisms occur in a variety of taxa in all biological kingdoms1 and distinguishing asexually propagated genotypes is essential for the understanding of their population biology. Among the higher fungi, however, the clonal 'individual' is especially difficult to define2 because most of the fungal thallus consists of a network of anastamosing hyphae embedded in the substratum. Whether fruit-bodies, the most recognizable part of a fungus, are produced by a single supporting mycelium can only be determined by establishing direct physiological continuity or genetic identity. We report a means by which individual fungi can be unambiguously identified within local populations and identify an individual of Armillaria bulbosa that occupies a minimum of 15 hectares, weighs in excess of 10,000kg, and has remained genetically stable for more than 1,500 years. © 1992 Nature Publishing Group.

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