What is the ecological relationships between fern and weed?

You wish to compare a fact with a concept. 'Fern' is the identifying name of a particular series of related plants whereas 'weed' is a subjective description based upon plant species that each individual attributes to any small plant. Hence a dandelion might be grown as a salad plant by one and be attacked by another for disfiguring his immaculate lawn. If you wish to make a comparison of fern with another plant variety you must select an appropriate group, e.g. compositae or mosses or lichens etc.