Fern adv. : Long ago.

Fern a. : Ancient; old. [Obs.] "Pilgrimages to . . . ferne halwes." [saints].

Fern n. : An order of cryptogamous plants, the Filices, which have their fructification on the back of the fronds or leaves. They are usually found in humid soil, sometimes grow epiphytically on trees, and in tropical climates often attain a gigantic size.

Example:
How to bring an asparagus Fern back from the dead?

Taxonomy
ferns, plants, Family, seed plants, Tree ferns, gametophytes, leptosporangiate ferns, species, spores, frond, pteridophytes, prothallus, leaves, whisk ferns, vascular plants, habitats, fiddleheads, Filicopsida.

Defination from the web:
fern is any one of a group of about 20,000 species of plants classified in the phylum or division Pteridophyta, also known as Filicophyta. ... This can be confusing since members of the fern phylum Pteridophyta are also sometimes referred to as pteridophytes. ...