Most easily identified by its Christmas-stocking-shaped individual leaf-like structures, the Christmas fern (Polystichum acrostichoides) retains its dark green foliage throughout the year, including at Christmas-time. In winter, a hinge-like structure on the evergreen fronds allows them to flatten against the ground, providing some insulation against the cold and more surface area for photosynthesis. The fern is a larval host for a recently discovered species of moth, Herpetogramma sphingealis, which is closely related to the serpentine webworm moth. Like many other ferns, this species spreads slowly via rhizomes. Tolerating a variety of habitat conditions, the Christmas fern thrives in forest understories with part shade to full shade in moist soils, but it is resilient against drought. At Glenstone, Christmas fern is found along the Woodland Trail and around the path near Tony Smith's Smug, 1973/2005.

–Tim Curley and Bonne Di Giansante