Know Your Natives – Christmas Fern

Christmas fern (Polystichum acrostichoides) of the Wood Fern (Dryopteridaceae) family prefers shady areas of deciduous woodlands and embankments with well drained, moist sandy to rocky soils. Christmas fern is found throughout much of the eastern half of the U.S., westward to Texas, Kansas and Minnesota. In Arkansas, it occurs statewide. Ferns in this family have round sori (singular: sorus, the technical term for a “fruit-dot” or cluster of spore-producing sporangia) occurring in rows, thus, the genus name which means “many rows.” This medium size “coarser” fern has large glossy green fronds (leaves) throughout the year making it ideal for Christmas decorations, including wreaths.

Christmas fern in a natural setting is found as individual plants in loose colonies or widely spaced individual plants. Plants have an upright central rootstock from which fronds grow in fountain fashion. Clumps of this long-lived fern increase in size over time, but the plant retains an overall circular shape. These large, easily noticed plants represent the sporophyte phase of the fern life cycle, during which spores are released to germinate into the tiny (about thumb-nail sized) gametophyte phase, during which gametes (sperm and egg) are produced. The gametes fuse at fertilization to form a new sporophyte plant. (A remarkable characteristic of this phase of the fern life cycle is that the sperm actually swim–in rainwater or a film of dew–to find and fertilize the egg.)

The rootstock of the sporophyte has one to several growth points with a group of fronds from each position. New fronds in early spring appear as tightly curled, silvery spirals referred to as fiddleheads* which uncurl to produce pinnate fronds. Fronds, up to two feet long and four inches wide, are robust, having 40 to 60 leathery, glabrous pinnae (leaflets) per frond. Overall shape of fronds is lanceolate with greatest width at mid-frond. Pinnae, with very short off-centered petiolules (stalks) that are perpendicular to the lighter green colored rachis (main axis of frond), are mostly alternate, but may appear to be opposite or actually be opposite. The upper pinnae surface is dark green while the lower surface is a lighter green similar to the rachis. Pinnae, up to 2 inches long, are undivided (as compared to once-, twice-, and even thrice-divided pinnae of other ferns) with serrated to entire margins. Each pinna has a characteristic single auricle (ear-like lobe) on the up-rachis side. From mid-rachis, spacing between pinnae gradually increases toward the petiole and decreases toward frond apex. Pinnae near the acuminate apex overlap. The lowest pair of pinnae is bent downward. Fronds have rachises (midribs) with a central shallow groove. Petioles and rachises are covered with dense, persistent light brown scales and filaments, much more so near the rootstock. Sterile and fertile fronds are erect to arching in spring, but by winter and during dry periods, fronds lie closer to the ground, often totally prostrate. With new fronds having grown, old fronds quickly become dry and soon lost in the duff (leaf litter).

Christmas Fern - Polystichum acrostichoidesPhoto 1: Tightly curled fiddleheads of Christmas fern in mid-March are well protected from the elements by scales and hairs.

Christmas Fern - Polystichum acrostichoidesPhoto 2: Fiddleheads in late March uncurling in response to warming temperatures.

Christmas Fern - Polystichum acrostichoidesPhoto 3: In early April, new fronds are mostly uncurled and erect while older, reclined fronds remain green for a short time.

Fronds are either fertile or sterile. Fertile fronds, surrounded by sterile fronds, stand more erect and are longer. Sori, also called fruit-dots, occur in two rows on the underside of pinnae on the upper third of fertile fronds. These spore-bearing pinnae are significantly smaller than other pinnae on the plant. This abrupt change of pinna size on fertile fronds is characteristic of Christmas fern. The upper portion of fertile fronds slowly withers after the indusium (protective cover over sporangia) dries and dust-like spores have been released.

Christmas Fern - Polystichum acrostichoidesPhoto 4: Upper surface of a sterile frond (left) and a fertile frond (right). Note the auricles, off-centered petiolules and smaller sporangium-bearing pinnae.

Christmas Fern - Polystichum acrostichoidesPhoto 5: Lower surface of same sterile and fertile fronds as in Photo 4. In this mid-November photo, the spores have already been released from the sporangia in the two rows of sori.

Christmas fern is ideal in a shady garden, in the shade of a wall or for shady naturalized areas where well drained, moist soils are found. Other than providing shelter for wildlife, the fern is not noted for providing significant other benefits to wildlife. However, its year-round strong character and long-term dependability as a clumping-fern makes it an ideal accent plant. Additionally, with arching leaves and retained old leaves, the plant can provide erosion control on slopes. Christmas fern is deer resistant. Fronds may be used in flower arrangements at Christmas or any other time of the year.

* Unfurled fronds referred to as “fiddleheads” based on appearance being similar to ornamentation on violins. Also referred to as “croziers” based on appearance being similar to shepherd’s staff.

Article and photographs by ANPS member Sid Vogelpohl

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