Walking fern is a perennial nonflowering vascular plant with distinctive, long-triangular leaves with a pair of lobes at the base of the blade. The leaves are simple, narrowly triangular, with netted venation. The leaves take root at the elongated tips, forming new plantlets. This fern’s sporangia (spore-producing organs) are grouped into sori (clusters) that are scattered on the underside of the leaves, attached on one side along the veins. Spores are produced May–October.
Similar species: There are 8 Asplenium species in Missouri, but the others look more like typical ferns, with compound leaves.
One close relative, ebony spleenwort (A. platyneuron) is a common forest-floor fern. When it grows near boulders and bluffs where walking fern lives, the two sometimes hybridize. The resulting sterile hybrid is called Scott’s spleenwort (A. x ebenoides). The basal halves of its leaves are much like typical ferns — pinnately compound (feather-compound) — but with the pinnae (leaflets) and lobes irregular in size. In the upper half, however, the leaves are uncut, resembling the leaf tips of walking fern and, like walking fern, sometimes taking root at the tips. The petioles (leaf stalks) are shiny and reddish brown to dark brown.
Sometimes, Scott’s spleenwort can bear leaves that are mostly lobed, and in a regular pattern. These specimens might be confused with lobed spleenwort (A. pinnatifidum), an uncommon eastern Ozark species. Lobed spleenwort’s leaves are shaped overall like those of walking fern, but they are deeply lobed yet not truly compound. Lobed spleenwort’s petioles are brown at the base, and dull green above (not brownish and shiny as in Scott’s spleenwort).
Leaves: typically 6 inches long, 1 inch wide at base; can reach nearly 16 inches long.
Common nearly statewide, although less common north of the Missouri River.
Habitat and Conservation
Walking fern grows in ledges and crevices of shaded dolomite and limestone bluffs and boulders. It is rarely found on acid substrates (such as sandstone and granite). Most people see it growing on shaded, moss-covered limestone outcrops and boulders, on cool, moist, north-facing slopes. It occasionally grows on the ground or on the decaying trunks of fallen trees.
Because of its unique leaves, some botanists have put walking fern into its own genus, Camptosorus. But because it forms hybrids with other Asplenium species and shares other similarities with members of that genus, most botanists agree it should be grouped with them.
Looking at a colony of walking ferns, it’s easy to see how they can reproduce and spread vegetatively, with the older plants surrounded by their offspring plantlets that take root from their leaf tips.
But like other ferns, this species has a two-parted life cycle. The plants we usually see are the sporophyte generation — they produce spores, which germinate to become tiny, flat, green, heart- or kidney-shaped plants. These are called gametophytes, because they produce gametes (eggs and sperm, from separate structures). The sperm require water to swim to the eggs. The fertilized eggs develop into new sporophyte plants, completing the life cycle.
Walking fern is one of the most easily identified Missouri ferns. You can spot it right away, as it grows on contrasting green, moss-covered boulders. This odd little fern can be a charming companion for hikers or people on float trips.
The name “spleenwort” arises from an ancient belief that any plant that had a structure shaped like a human body part could be used medicinally to treat ailments for that body part. Although that idea is now disproven, people once took the notion very seriously. And because the spore clusters of Asplenium species were spleen-shaped, people thought these plants might heal diseases of the spleen. “Wort,” used in many plant names, is an old word for “herb.”
Asplenium species occur worldwide. Missouri’s spleenworts all belong to a subgroup called the “Appalachian Asplenium Complex,” which is one of the most intensively studied groups of ferns in the world.
Botanists have noted that spleenworts very commonly form hybrids with each other. Then, the first-generation, sterile hybrids can sometimes regain fertility through a process of chromosome doubling. The fertile species called lobed spleenwort (A. pinnatifidum) originally started long ago as a hybrid between walking fern and another species, mountain spleenwort (A. montanum).