or Rustyback, in botany, a genus of the cryptogamia filices, of which there are 30 species, but only three of them natives of Britain, viz. the septentrionale, or horned fern, which grows on walls or cliffs of rocks; the ilvene, or hairy fern, growing in cliffs of rocks; and the thelypteris, or marshfern, in turfy bogs.