I also get ferns as weeds in my work greenhouse. Very common in a wet/humid environment. Mostly Dryopteris, Thelypteris, Nephrolepis, Phlebodium, Pellaea, Pyrrosia, Psilotum, and Adiantum.
For me, it's really interesting because our teaching collection with the ferns is in a completely different greenhouse from the CPs. I weed out ferns from the CP room. The only way I can explain how those ferns repeatedly germinate their spores in the CP room is for the spores to have been blasted from one greenhouse to another through the exhaust fans.