a small, hardy fern (Polypodium virginianum) of the most common family (Polypodiaceae) of ferns, with densely matted, creeping stems, found on cliffs and walls in E North America and often grown in gardens
See wall fern in American Heritage Dictionary 4
noun
A low-growing Eurasian fern (Polypodium vulgare) characterized by creeping stems that form dense mats.