Most fungi are able to reproduce both sexually (via meiosis) and asexually (via mitosis) by means of spores. Spores are often produced in huge numbers and vary in shape and size depending on environmental conditions. Moulds engage in asexual reproduction, whereas mushrooms are the fruiting bodies that produce sexual spores. One of the main objectives of the sexual stage is long-term survival, whereas dispersal is the main purpose of the asexual stage.
The broad distributions of many fungal species is linked to their production of spores, which often travel thousands of kilometres through the air before they land and germinate. Water and animal vectors can also lead to the transfer of spores. Because their plant hosts are often sparsely distributed in the Arctic, effective spore formation and dispersal is essential to survival. Arctic fungi have developed spores that are resistant to many environmental extremes, and thus better adapted to life in the harsh northern climate. For example, the spores of many arctic species can survive freezing, starvation, and desiccation, grow at temperatures as low as -5°C, grow and reproduce during periods of water stress, tolerate oxygen concentrations as low as 2% (the air we breathe is 20% O2), and survive in both acidic and alkaline conditions (pH 1–9).