Growth or Body Forms
Lichens take on many different shapes. These shapes reflect how the lichen is organized internally. Some lichenologists divide the lichens into seven or eight different body types, other choose to use five types. For people new to lichens it is best to divide them into three forms: crustose, foliose and fruticose. On this web site, Lichens.ie, four types are used, the additional one being the Cladonia group. Strictly this is not a body type, but is used on this web site for its easily identifiable ‘pixie cup’ structure.
Crustose lichens often look like splashes of paint on rocks or trees; they form a very thin crust on the substrate and cannot easily be removed intact. They usually lack a lower cortex (see Anatomy). A common crustose lichen found in Ireland is Ochrolechia parella. For a description of this species click here.
Another common crustose lichen is Lepraria incana. It is found on damp walls / soil and forms a ‘powder’. It is so amorphous that it is not easy to see a distinct cortex or medulla when examined under a microscope.
Foliose lichens are leaf-like and can usually be relatively easily detached from the substrate undamaged. They often have a distinct structure that attaches them to the substrate, such as a holdfast or root-like rhizines. They usually have a distinct upper and lower cortex, with a medulla in between, similar to the diagram in the section on Anatomy. One of the most dramatic of the Irish foliose lichens is Lobaria pulmonaria. Individual lobes may be 25 cm in length; it is an indicator of ancient forests.
Fruticose lichens are usually hanging (pendant) or upright. It is difficult to see any distinct upper or lower surface (radially symmetrical); usually attached to the substrate at a single point; some may be unattached. They are the group most sensitive to air pollution. A common fruticose lichen found in Ireland’s woodlands is Usnea flammea.