How a long-lived fungus keeps mutations in check

An individual of the mushroom-forming fungus Armillaria bulbosa is among the largest and oldest of all living organisms: More than 1500 years old, it covers more than 15 ha and weighs more than 10,000 kg (1). Some trees can also reach ages of thousands of years (2). How can such long-lived organisms keep the number of deleterious mutations during somatic growth in check? In a recent paper in Mycologia, Anderson and Catona (3) report extremely low genetic variation, and by inference a very low mutation rate, in a long-lived individual of another fungus, Armillaria gallica (see the photo). This genomic stability is puzzling and unexpected, because the sequenced samples come from locations that are more than 100 m apart and presumably separated by many rounds of cell division