FILICES, (from filum, "a thread," quasi filatim incisa), FERN; one of the seven tribes or families of the vegetable kingdom, according to Linnæus, by whom it is thus characterized: "having their fructification on the back side of the frondes." They constitute the first order in the class cryptogamia; and consist of 16 genera, which are divided into fructificationes, spicatae, frondosæ, et radicales. This order comprehends the entire 16th class of Tournefort, in whose system the filices make only a single genus, in the first section of the above-mentioned class.