Article and photos by Katherine Wagner-Reiss

Christmas fern, each frond with 20–35 pairs of pinnae (leaf segments). Notice the brown sori (clusters of spore cases) covering the undersides of the upper pinnae on the fertile fronds.

Auricles protruding from the bases of the pinnae (leaf segments), produce a “Christmas stocking” or “Santa’s boot” appearance. An auricle is a plant part likened to an ear.

The Christmas fern earned its name because, as one of the few native ferns that is evergreen, it is available as a Christmas decoration; in addition, one can imagine that each of its leaf segments looks like a traditional Christmas stocking or even Santa’s boot (see photo).

The scientific name is Polystichum acrostichoides. Polystichum means “many in a row,” referring to its sori (clusters of spore cases) being arranged in rows on the backsides of fertile leaf segments (see photo). The placement, size, and shape of sori were the major way that fern genera were differentiated in 1800, when the name Polystichum was assigned.

The epithet acrostichoides means “similar to Acrostichum.”  Acrostichum is a fern genus characterized by having its spore cases distributed as a dense uniform mass on the undersides of its leaf segments, rather than having them organized into discrete sori. Although Christmas fern does have sori, they are so crowded together that they superficially appear as a uniform mass; hence acrostichoides (see photo).

Polystichum acrostichoides is a fern for the shade or part shade garden; it grows in clumps that enlarge over time. It is tolerant of moist or dry soil and of deer and rabbits. While typically found singly or in groups of two or three in the wild, it can be planted en masse for erosion control. You can find Christmas fern at the Morris Arboretum on a shady little path between the back of the Rose Garden and the Fernery (see photo). You will also find it in woodlands throughout eastern North America. The fertile fronds with sori are seen June through October; in the winter you will still see the dark green vegetative fronds. In spring, the inedible fiddleheads (i.e. unfurling new leaves that look like the ornamental scroll at the top of a fiddle) emerge.

P.S. Perhaps my personal story can inspire you to think of the Morris Arboretum as a wintertime destination. In order to get my Botany Certificate from the New York Botanical Garden, I took a class called “Native Flora in Winter.” I spent a lot of that winter outside; I enjoyed every experience, despite not being a fan of cold weather. Dress in layers, don’t stay out too long, and finish with a hot drink: you’ll be happy you got outside to examine evergreens like Christmas fern!

Katherine has her Certificate in Botany from the New York Botanical Garden and is a botanical tour guide and freelance writer.

Polystichum acrostichoides: Polystichum means “many in a row” referring to the brown sori (clusters of spore cases). The sori are so crowded together that they give an acrostichoid appearance (see text).

Polystichum acrostichoides (Christmas fern) located along this woodland path leading down to the Fernery.