Frond: the leaf of a fern
Pinnae (singular= pinna): the "leaflets" of fern fronds ("leaves")
Pinnule: A secondary pinna ("sub-leaflets")
Rachis: The upper part of the fern petiole, where the pinnae are found
Rhizome: underground stem part of the fern, usually is horizontal
Stipe: The stalk below the blade in ferns