Lady fern (Athyrium filix-femina), also known as the alpine lady fern, is an uncommon plant in Colorado but can be found in 49 out of 50 states, excluding Hawaii, making it one of the most abundant ferns in the U.S. The telltale mark of a lady fern are clusters of reddish or bright green sori, or spore sacs, on the underside of its almost lacy, feathered fronds. These sori identify the filix-femina as a pteridophytes, a group of vascular plants that reproduce by spores rather than seeds.