Know Your Natives – Lady Fern

Lady Fern (Athyrium filix-femina*) of the Woodsiaceae (Lady Fern) family is a medium size fern of North America, Europe and Asia. The genus name originates from a Greek word referring to “door” in reference to the hinged indusia (protective spore covers). The specific epithet is based on Latin words for “fern” and “woman.” Lady fern occurs across the U.S., including Alaska, as well as Canada. In Arkansas, lady fern is the only species of Athyrium and is found statewide. Preferred habitat is shady sites with moist to wet soils: rich woods, seeps, springs, moist areas of prairies, and at swamp and drainage borders. The common name relates to the graceful appearance of this “delicate” fern, as compared to “coarse” ferns, such as male fern (Dryopteris filix-mas).

Lady fern is a hardy deciduous fern with shallow horizontal rhizomes to ¾ inch thick. Rhizomes produce new fronds (leaves) at their growing tips, with the bases of old fronds persisting for up to four years. Numerous wiry roots, with their lateral rootlets, grow from all sides of the rhizomes. Rhizomes of a mature plant occasionally divide, ramifying and rooting through the soil, to form a dense mat.

Photo 1: The divided rhizome of this single plant is hidden by densely packed wiry roots. Buds of new fronds can be seen in the middle portion of the mat (16 inches by 7 inches) and at its left edge. Photo – February 5.
Photo 2: This rhizome divided into a left and right “limb” (spread equals 9½ inches) from its “point of origin” at bottom of photo. New growth occurs at ends of limbs. Bases of dead fronds are persistent, but decay year-by-year.

In early spring, tightly coiled fronds, pinnae (leaflets), and pinnules (secondary leaflets) emerge as “fiddleheads.” Protective papery elongate scales along the stipe (frond stalk), and the stipe itself, are reddish brown.

Photo 3: Early fronds or “fiddleheads” have reddish scales along the stipe.
Photo 4: Fiddleheads quickly develop into limp ascending fronds. Photo – April 2.

Ovate-elliptic fronds mature to 3 feet long and 10 inches wide; pinnae are narrower in shape and lanceolate-oblong. Fronds are light green above and below. Largest pinnae (5+ inches long and 1+ inches wide) are located near the middle of the rachis (pinna-bearing axis). Except for the two lowermost pinnae, which tend to be opposite, pinnae (20+ along both sides of rachis) are alternate. Size and separation of pinnae decrease distally, ultimately merging to form a fine-pointed apex. Fronds are mostly glabrous, except for the scales along the stipe, as noted above. The rachis is rounded on the lower side and flat with a central groove above. The stipe may be half as long as the rachis.

Photo 5: Fronds and pinnae. Viewed from above, fertile and sterile fronds (as shown) have the same appearance. Photo – October 18.

Lady fern’s compound fronds are described as bipinnate to bipinnate-pinnatifid. The ultimate divisions, the pinnules, to ½ inch long and 3/16 inch wide, are sharply toothed with secondary veins terminating at the tips of the teeth.

The ferns are an ancient group of plants with a dominant presence in the fossils of the Coal Age, some 350 million years ago. And they remain, with their vascular tissues that transport water, minerals, and sugars, a prominent and competitive group in today’s modern flora. But unlike almost all of the modern plants we see around us, they have no seeds and no flowers. Instead, their life cycle is characterized by spores and by two quite different kinds of plants, one that produces those spores and the other, the prothallus, that produces swimming sperm.

Lady fern has separate fertile and sterile fronds, with the same adaxial appearance. To find the fertile fronds, you turn them over to see the lower surface, which bears tiny clusters of spore-producing sporangia called sori (singular, sorus) or fruit-dots. Crescent- to oval-shaped sori are arranged in two rows on either side of the midrib of the larger pinnules. Early in development, the sori are partially covered by a translucent, hinged indusium. As spores develop, indusia dry and shift away to expose the sporangia and facilitate spore dispersal.

Photo 6: The abaxial side of this fertile frond’s pinnules bears developing sori with translucent indusia. Photo – May 23.
Photo 7: Abaxial sides of a sterile and fertile frond are shown. The short-stalked pinnae are lanceolate-oblong with a wide base. Margins of pinnules are toothed. Photo – November 30.
Photo 8: Pinnules have pinnate venation with secondary veins terminating at tips of teeth. Sori occur in rows between midrib and pinnule margins. As shown, the sporangia of the sori are exposed and poised for spore dispersal. Photo – October 18.

With dispersal of spores, the reproductive activity of the “sporophyte” phase of a fern’s life cycle concludes. In the soil, spores germinate to produce a prothallus, the “gametophyte” phase. The tiny prothallus produces gametes, sperm and egg. Sperm swim through ground moisture to fertilize eggs that have remained attached to the prothallus. Fertilization produces a zygote that, in turn, develops into a new sporophyte plant––the plant that we recognize as a “fern.”

For a shady to partially shady garden or natural area that has moist to wet soils, this delicate-cut fern should be considered. Plants have an airy appearance and provide nice contrast with coarse ferns and broad leaf plants. The weak fronds are easily damaged by wind and passing animals. Plants go dormant early with dry soil conditions. Lady fern expands slowly by rhizome growth, but is not aggressive. For a similar appearing fern that is more compact, prefers drier soil, and tends to be evergreen, Marginal Wood Fern (Dryopteris marginalis), may be an alternative choice.

Photo 9: Natural seeps along this abandoned creek bed provide low-flowing, standing water or moist soil throughout the year, optimal habitat for lady fern. Photo – April 1.
Photo 10: Fifty days later than above photo and along the same seep, plants have reached their mature height. Photo – May 23.

*Across its circumglobal range, lady fern has many variations. Two subspecies have been classified in the eastern U.S.: Southern Lady Fern (Athyrium filix-femina subsp. asplenioides) and Northern Lady Fern (Athyrium filix-femina subsp. angustum). These subspecies, which some authorities elevate to species, are distinguished by the location of the broadest widths of the fronds (closer to the base versus closer to the middle) and spore color, among other characters; however, variations do occur. The Arkansas subspecies is southern lady fern, although the range of northern lady fern approaches the state closely in Missouri and may occur within northern Arkansas.

Article and photographs by ANPS member Sid Vogelpohl

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