Although some ferns are naked, many have fronds that are covered in hairs (one cell wide) and/or scales (more than one cell wide). These are most dense on the unfurling frond (the koru or fiddlehead), and probably have a protective function. In New Zealand, there are several species-pairs of filmy ferns where the upland species of harsher habitats has hairs while the lowland species is naked.

Along with the shape of the reproductive features, the presence and nature of scales and hairs are very important in identifying ferns, both in separating closely-related species and in distinguishing major groups. The two groups of tree ferns in New Zealand are easily distinguished because the Cyathea species are scaly whereas the Dicksonia species are hairy. See the third image down at this link: http://blog.tepapa.govt.nz/2009/03/06/whats-a-punga/

Scales are often fairly boring, being a uniform brown and with smooth margins. But the scales of this new tangle fern, with their dark centre and ciliated margins, are quite remarkable! Almost looks like a little animal…