What does it mean if a lichen is described as crustose?

When a lichen is described as crustose, it means that it grows closely attached to surfaces, often binding tightly to the substrate such as rocks, bark, or soil. This attachment creates a crust-like appearance, making it difficult to peel or remove from the substrate. Crustose lichens typically have a flat, compact structure that integrates with the surface, rather than forming distinct, separate layers or shapes. This characteristic allows them to thrive in harsh environments where other organisms might struggle, as their intimate contact with the substrate helps them absorb nutrients and moisture efficiently.

The other choices pertain to different types of lichen growth forms. For example, a bushy appearance is indicative of foliose lichens, which have leaf-like structures. Living in deep layers of soil pertains to specific adaptations of certain plants or fungi, not lichens. Large fruiting bodies relate to different reproductive structures found in some fungal species, but are not representative of crustose lichens.