FILICES, (from filam "a thread," quasi filatim incisum), FERNS; 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, frondosae, & radicales. This order comprehends the entire xvth class of Tournefort, in whole system the filices make only a single genus, in the first section of the above-mentioned class.