The common name refers to the practice of gathering the evergreen leaves during Christmas time as a holiday decoration. This attractive fern is fairly easy to identify because of its scaly stalks and leathery leaflets with asymmetrical bases. It is the only Polystichum sp. in Illinois. A related species, Polystichum braunii (Braun's Holly Fern) is typically found in the conifer forests of the north. This latter species has bipinnate or pinnate-pinnatifid leaves and its ultimate leaflets have stout sharp teeth. Thus, it has a very different appearance from the Christmas Fern. Some Asplenium spp. (Spleenworts) superficially resemble the Christmas Fern because of their simple pinnate leaves. However, the Spleenworts are smaller in size (up to 1½' tall) and more delicate in appearance; the stalks of their leaves are not conspicuously scaly and the margins of their leaflets lack the narrow fine teeth of the Christmas Fern.

This native perennial fern is 1½–2½' tall, consisting of a loose rosette of several leaves that are erect to ascending. The leaves are up to 2½' long, 5" across, simple pinnate in their structure, and evergreen. Fertile leaves are longer than infertile leaves. Each leaf has 20-40 leaflets, which are arranged in two ranks on either side of the rachis (or central stalk); each leaf is oblong or oblong-lanceolate in its overall shape. Most of the leaflets are arranged alternately along the rachis of the leaf; they are medium green, lanceolate, hairless, leathery, and rather lustrous in appearance. The margins of each leaflet have narrow fine teeth that are spaced moderately apart from each other. The base of each leaflet is often asymmetrical – one side is longer and more pointed than the other. The veins of each leaflet are pinnate; they are straight, but not very conspicuous. Each leaflet also has a short petiole (more properly, a petiolule). The rachis (or central stalk) of each leaf is rather stout and conspicuously scaly; these membranous scales are dull white to light brown. The petiole is shorter than the rest of the compound leaf; it is also rather stout and even more scaly than the rachis. The sori (spore-bearing structures) are restricted to the upper leaflets of the fertile leaves; they are round and reddish brown. The sori can be found in two rows along the central vein and near the terminal points of lateral veins on the underside of each leaf; sometimes they cover the entire underside of a leaflet. The sori develop and release their spores during the summer or early fall. The root system consists of a stout dark rhizome with remnants of leaf stalks above and abundant fibrous roots below. Plants can occur individually or in small loose colonies.

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

The Christmas Fern is occasional to locally common in southern and central Illinois, becoming uncommon in northern Illinois. Habits include rocky upland woodlands (deciduous), bluffs, slopes of wooded ravines, and shaded cliffs. This fern is especially likely to be found where either limestone or sandstone comes close to the ground surface.

Polystichum acrostichoides is a common species most closely related to P . munitum (G. Yatskievych et al. 1988), which also occurs extensively on forest floors. 

 The dimorphic pinnae of Polystichum acrostichoides are not unique to the genus; they are found also in some Asian species. Numerous variants have been named, mostly as forms, but none are of taxonomic consequence. Hybrids are known with P . braunii ( P . × potteri Barrington) and P . lonchitis ( P . × hagenahii Cody). The latter hybrid is rare, known only from its type locality in Ontario, where it grows with both parents. It is recognized by its intermediate morphology (leaves wider than P . lonchitis , narrower than P . acrostichoides , with slightly contracted sorus-bearing pinnae) and malformed sporangia and spores. Polystichum × potteri is much more widespread, from Nova Scotia, New Brunswick, and Quebec through New England to Pennsylvania. It resembles P . braunii but has narrower leaves bearing malformed sporangia.

Stems erect. Leaves dimorphic (only in this species); fertile pinnae distal, much contracted; sterile leaves arching, 3--8 dm; bulblets absent. Petiole 1/4--1/3 length of leaf, densely scaly; scales light brown, diminishing in size distally. Blade linear-lanceolate, 1-pinnate; base narrowed. Pinnae oblong to falcate, not overlapping, in 1 plane, 2--6 cm; base oblique, acroscopic auricles well developed; margins serrulate-spiny with teeth ascending; apex acute or blunt with subapical and apical teeth same size; microscales filiform, lacking projections, dense, on abaxial surface only. Sori confluent, completely covering abaxial surface of pinnae (only in this species); indusia entire. Spores light brown. 2 n = 82.

Nephrodium acrostichoides Michaux, Fl. Bor.-Amer. 2: 267. 1803

Forest floor and shady, rocky slopes; 0--1500 m; N.B., N.S., Ont., P.E.I., Que.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Vt., Va., W.Va., Wis.; Mexico; naturalized in Europe.

The Christmas Fern is occasional to locally common in southern and central Illinois, becoming uncommon in northern Illinois. Habits include rocky upland woodlands (deciduous), bluffs, slopes of wooded ravines, and shaded cliffs. This fern is especially likely to be found where either limestone or sandstone comes close to the ground surface.

During the winter, the fronds of this evergreen fern may be eaten sparingly by White-Tailed Deer. Young fronds may be eaten by some upland gamebirds (Ruffed Grouse, Wild Turkey), otherwise this species has little value to wildlife.

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 1
Species: 2
Species With Barcodes: 1

Rounded Global Status Rank: G5 - Secure

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

The preference is light shade, moist to slightly dry conditions, and soil that is loamy or rocky with abundant leaf mould.