Crustose is a habit of some types of algae and lichens in which the plant grows tightly appressed to a substrate forming a biological layer of the adhering organism. Crustose adheres very closely to the substrates at all points. Crustose is found on rocks and tree bark. Some species of marine algae of the Rhodophyta, in particular members of the order Corallinales, family Corallinaceae, subfamily Melobesioideae with cell walls containing calcium carbonate grow to great depths in the intertidal zone, forming crusts on various substrates. The substrate can be rocks throughout the intertidal zone, or, as in the case of the Corallinales, reef-building corals, and other living organisms including plants, such as mangroves and animals such as shelled molluscs. The coralline red algae are major members of coral reef communities, cementing the corals together with their crusts. Among the brown algae, the order Ralfsiales comprises two families of crustose algae.
Many lichens also grow close to the surface of rocks, tree trunks and other substrata, and are referred to as crustose lichens. Crustose organisms can be detrimental to engineered structures when found on buildings, coastal structures, and ships.
There are different types of Crustose Lichens, including endolithic, endophloidic and leprose. Endolithic lichens are immersed in rocks with their bodies above the surface. Endophloidic ones are located in plant tissue. Leprose lichens are crusts without a layered structure. 
Crustose has learned to adapt to its environment. The environment it is currently adapting quite well to is the dry and drought resistant climates. It has seen to work well in deserts, ice free parts of Antarctica and in the Alpine and Arctic regions..
Crustose can come in a variety of colors such as yellow, orange, red, gray and green. These colors tend to be bright and vibrant.
Crustose is similar to other lichens because they share a similar internal morphology. The lichen's body is formed from filaments of the fungal partner. The density of these filaments determines the layers within the lichen. 
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