Linked from
The 7 pages that link to Apothecium, each with the reason it gives.
AscusRelated: Its asci release spores from an exposed hymenium.
Fruticose lichenRelated: Many fruticose lichens form apothecia on their branches or branch tips.
UsneaRelated: Usnea species can form apothecia that produce fungal spores.
LecanoralesRelated: Many Lecanorales produce spores in conspicuous apothecia.
Parmotrema perlatumRelated: Sexual reproduction in lichen fungi can occur in apothecia.