Lichens can occur anywhere on land, and some can live in aquatic environments. The nearest rock, wall or roof probably has lichen on it. Often the lichen is mat-like, and clings to the surface. Some are like little bushes: see the photos. Lichens are famous for not needing a regular supply of water; their metabolism can go into suspension, and later revive. When growing on mineral surfaces, some lichens slowly break down the substrate, and extract tiny amounts of mineral nutrient. Fungi form the main part of the thallus (body), with the photobiont contributing 20% or less. The photobiont is usually on the inside of the thallus.