Final answer:
The fungus in a lichen is most commonly a member of the Ascomycota, or cup fungi, but can also sometimes be from the Basidiomycota, club fungi. Lichens exhibit various forms such as crustose, foliose, and fruticose with unique spore-dispersal structures.
Step-by-step explanation:
The fungus in a lichen is most commonly a member of the Ascomycota, known as cup fungi. Lichens are complex organisms that arise from the symbiotic relationship between a fungus and a photosynthetic partner, usually an algae or cyanobacterium. The fungal component of a lichen is known as the mycobiont. Sometimes, lichens can also have a fungal partner belonging to the Basidiomycota, which are the club fungi. Lichens come in various forms including crustose, foliose, and fruticose types, each with a different morphology. The fungal partners in these lichens create unique structures for spore dispersal. In contrast, Zygomycota, another division of fungi, and mycorrhizae, which are symbiotic associations between a fungus and the roots of a vascular host plant, are not typically involved in forming lichen.