This is a large family containing many genera. The relationship between them is not so obvious.
Campanella is a small, tough saprophytic fungus found attached laterally on twigs and small dead branches in humid habitats.
These small saprobic fungi are found on fallen plant material and have a Marasmius-like fruiting body with a felty cap surface consisting of thick-walled dextrinoid hairs. A hand lens is needed to see them.
Oddly, it's not clear as to what family this genus belongs to. When looking around, I found it placed in Marasmiaceae, Pleurotaceae, and here in the Tricholomataceae.
These are saprophytic on dead plant material, commonly found on decaying wood or leaf litter. They often appear in large numbers after rain, which shrivels up when dry and quickly rehydrates when wet. They are usually distinguished by their black or dark stipe.