Fungi are generally saprobes or parasites, except lichens, which rely on symbiotic algae. They have cell walls and feed by external digestion and absorption. Most develop into massed filaments called hyphae, which grow into dead or living material, but some have reverted to single cells such as yeasts.

Even larger fungi like mushrooms are generally inconspicuous except for spore-forming stages. In a few kinds the spores have a posterior flagellum, but most are non-motile and rely on wind, water, or animals for distribution. In sexual reproduction the nuclei usually do not fuse until just before spores are formed.

Ascomycota produce sexual spores inside enlarged cells called asci. In Eurotiomycetes these usually occur in cleistothecia, closed bodies which then crack or disintegrate to release them. However, in some sexual stages are rare or unknown.