[kruhs-tohs] 
| forming a crusty, tenaciously fixed mass that covers the surface on which it grows, as certain lichens. |
| crus·tose (krŭs'tōs') adj. Of or relating to a lichen whose thallus is thin, crusty, and closely adherent to or embedded in the surface on which it grows. [Latin crūstōsus, crusted, from crūsta, crust; see kreus- in Indo-European roots.] |
toʊs