The shield ferns were moved from Aspidiaceae to Polypodiaceae and then to Dryopteridaceae. Ferns have creeping or erect rhizomes that are often scaly. The leaves are called fronds and are stalked, erect or spreading. The leaf blades are curled in bud (fiddleheads) and are mostly divided compoundly. Ferns reproduce not by seeds but by spores and usually need abundant moisture for reproduction. The spore sacs are clustered toghether in something termed a sori and covered with a membrane (indusium) usually on the underside of the leaf.