Lowland brittle fern, or southern fragile fern, belongs to a fern genus that is confusing even for botanists. But most of us can identify this common fern rather quickly by its general shape, its springtime appearance, and its preference for soil (not rock ledge) habitats.
This is a relatively small, delicate, light green fern with leaves that are 1–2 times pinnately (feather) compound. In general outline, the leaves are lance- to ellipse-shaped, with the widest part at or near the middle.
The leaves emerge as a cluster from a point ½–2 inches behind the tip of the horizontal, rootlike rhizome (hence the scientific name protrusa, for the protruding rootstock; in related ferns, the leaves are clustered at the tip of the rhizome). The rhizomes are covered with tan or golden hairs, especially toward the outer tip.
Spores are produced in circular clusters scattered on the underside of the leaves. Before they mature, the spores are covered by a hoodlike, delicate, inflated structure (indusium) that attaches to the leaf on one side of the circle. These bladderlike, covering indusia give bladder ferns the name, but they usually wither and disappear by the time the spores are mature.
Spores mature in this species April–July.
Key identifiers:
- Springtime appearance; usually withers by late summer.
- Leaves emerge as a cluster from a point ½–2 inches behind the growing tip of the rhizome.
- The rhizomes are covered with tan or golden hairs, especially toward the outer tip.
- Light green, delicate-looking, lacy appearance.
- Occurs in moist, rich forest soils.
- Spores in circular clusters, scattered on leaf undersides.
Similar species: There are 3 additional Cystopteris species in Missouri. They all appear later in the season, and they all prefer rock-ledge (not soil) habitats.
- Bulblet fern, or bladder fern (C. bulbifera), has leaves that are triangular in outline (widest at the base), the stems are reddish tinged when young (turning green or straw-colored at maturity). Lobed, green bulblets often appear along the leaf’s midvein (rachis). These bulblets, which usually develop in early summer, can fall off later and grow into new plants. Scattered in the Ozarks and Ozark Border. Occurs on moist, shaded ledges of dolomite and limestone bluffs and outcrops (less commonly on rocky slopes in moist forests). Spores appear June–September.
- Tennessee bladder fern (C. tennesseensis) generally resembles bulblet fern, but it only rarely produces bulblets, and when it does, they are small, unlobed, and malformed. Petioles are dark brown toward the base. Nearly every leaf is fertile, with even the smallest leaves bearing spores. Scattered throughout the Ozarks and Ozark Border, and locally west and north, mostly in counties along the Missouri and Mississippi rivers. It is restricted to shaded rock outcrops and bluff ledges: dolomite, limestone, sandstone, chert, and granite. Spores are produced May–October.
- Mackay’s brittle fern (C. tenuis) is quite rare in Missouri and restricted to only two counties. Leaves, in general outline, are lance- or ellipse-shaped (widest at or near the middle), the leaves are clustered at the tip of the rhizome, and the leaf stems are usually dark brown at the base. It is uncommon in the eastern portion of the Ozark Border, in Jefferson and Ste. Genevieve counties. It occurs on ledges of moist sandstone bluffs. It produces spores June–September.
Leaf length: 3–16 inches, sometimes to 20. (Note that the related bulblet fern can reach 25 inches or more.)
Scattered throughout the state.
Habitat and Conservation
Mesic (moist) and bottomland forests in rich soil of lower slopes and bottoms of ravines, stream banks, and bottoms of sinkholes, on a variety of substrates.
Lowland brittle fern is the only Missouri fern in genus Cystopteris to occur principally in terrestrial (soil) habitats, and not on rock ledges. It’s a common springtime sight in mesic forests around the state, often growing among wood violets, spring beauties, and other spring wildflowers. In many areas, the leaves wither in late summer.
Status
One of Missouri's Cystopteris species, Mackay’s brittle fern (C. tenuis), is listed as a species of conservation of concern in our state, due to it limited range in Missouri. It is considered critically imperiled because in Missouri it is quite rare and lives only on sandstone bluffs. Elsewhere in North America it has been recorded from a variety of substrate types.
Taxonomy: Except for bladder fern, Missouri’s Cystopteris species were once all called “fragile fern,” C. fragilis. Today, that name in its strict sense applies only to a species that occurs north and west of Missouri, not in Missouri itself. In the past, many of the confusingly different Cystopteris ferns were all lumped together as different forms or varieties of C. fragilis. But DNA research has uncovered the genetic lineages of these groups, and botanists have determined they should be treated as separate species.
Also, in the distant past, many current species arose as hybrids among the related species. Complicating matters, several species and hybrids still combine to form intermediate offspring. If you find this genus confusing, you’re not alone!
Life Cycle
Ferns have a two-part life cycle. The part we usually see is the sporophyte, a plant that produces spores. When a spore germinates in the right environment, it matures to become a gametophyte. In the wood-fern family, the gametophyte part of the life cycle is tiny, green, flat, heart- or kidney-shaped, and often has stalked glands for producing gametes (eggs and sperm). When eggs and sperm unite, they become a new sporophyte plant.
This particular fern lives much like spring-blooming forest wildflowers, which grow and reproduce before forest trees develop new leaves and shade the forest floor. Like spring beauty, dogtooth violet, bloodroot, and Dutchman’s breeches, this fern sprouts from its rootstock, grows leaves, collects sunlight energy, and reproduces in early spring when sunshine still reaches through the tree branches. Then its leaves wither and it rests until next spring.
Human Connections
This is the little spring fern that fools your eyes when you’re hunting for morels in spring: on a bright spring day, its leaves cast ornate shadows. The honeycomb pattern of dark dots on tan, fallen leaves can look surprisingly like the dark-pitted texture of morels. And the ferns emerge about the same time as morels, too!
This is also the tender little fern that forms miniature bouquets on the forest floor with equally tender and beautiful spring wildflowers, amid lush green mosses — welcome sights after a cold winter!
In a fern genus that confuses even botanists, lowland brittle fern is easily recognized as a common springtime sight in moist forest soils.
Ecosystem Connections
This species can be threatened by invasive plants such as garlic mustard and bush honeysuckle, which grow in dense colonies and shade out this small fern, impeding it during the few months it is above ground to grow and reproduce.
This small fern, which loses its leaves and goes dormant before late summer, does not seem to be a principal food for many animals, although apparently some aphids, plus deer, turkey, and other vertebrates, may eat it.
Ferns and other nonwoody springtime plants are important members of a moist wooded-slope community. Even after their leaves have died away, their rootstocks help hold the soil in place, preventing erosion.
