Lichens are a type of symbiotic organism made up of a partner plant and a fungus. There are three main types of lichens: crustaceans, foliar and fructose, each with its own unique shape, structure and environmental preferences. Intermediate types include leprosy and flaky lichen, among others. These organisms can also be grouped according to the type of environment in which they prefer to grow.
Each individual lichen consists of a mycobiont, or fungus, associated with a photobiont or phycobiont in the form of green algae or cyanobacteria. Algae or bacteria perform photosynthesis, providing nutrients to the fungus and giving the lichen its characteristic greenish or bluish color. Both parts of the lichen get water and minerals from dust and rain, but some also get nutrients from their substrate through the fungal pair.
Not all types of lichens are the same. Crustaceans are flat, not lobed, are well attached to their substrate, and can be difficult to remove from the rock or tree where they grow. The leafy lichens have a more leafy appearance, as their name suggests, and consist of two thin mushroom leaves with algae in the middle. They grow in round-lobed formations and are easier to remove from their substrate, as they adhere only by small roots. The fruiting lichen or shrub has small, round branches made of fungi that contain algae and an unusual pattern of vertical growth that may look like a beard or small shrub.
Other types of lichen include leprosy lichen, which forms powdery masses, largely unstructured, with no smooth surface. Placodioid lichens are lobed or not attached to the edges and are well attached to the center, making them an intermediate form between crustaceans and leafy lichens. Another intermediate form, the scaly lichen, has many tiny lobes. Dimorphic lichens are characteristic of both scaly and fructose lichens, with small lobes bearing tiny stems or branches.
The environmental grouping divides lichens into seven broad categories. Various types of lichens grow on plants and are called epiphytes. This group includes corichol lichens, which prefer to grow on tree trunks, as well as branch lichens, which inhabit the branches. Musicocolos lichens grow on live moss, and leaf lichens prefer evergreens. Both types are epiphytic, but the lichens legnicols, saxicols, and soil, which inhabit wood, stones, and soil, respectively, are not epiphytes.