Definition of mule's fern in English:

mule's fern

(also mule fern)

noun

rare
  • Any of several ferns related to hart's tongue, Asplenium scolopendrium; especially the Mediterranean fern A. sagittata, with sagittate fronds.

Origin

Mid 17th century; earliest use found in Thomas Johnson (d. 1644), apothecary and soldier.