Lowland brittle fern, or southern fragile fern, belongs to a fern genus that is confusing even for botanists. But most of us can identify it rather quickly by its general shape, its springtime appearance, and its preference for soil (not rock ledge) habitats. It 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 rhizome (hence the scientific name protrusa, for the protruding rootstock; in related ferns, the leaves are clustered at the tip of the rhizome).
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.
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), and 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, occurring in 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.
Habitat and Conservation
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 carry out the business of living before forest trees grow 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.
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 (or southern fragile fern) is easily recognized as a common springtime sight in moist forest soils.
This species can be threatened by invasive plants such as garlic mustard and bush honeysuckle, which grow in dense colonies and can essentially shade out this small fern, impeding it during the few months it grows and reproduces, before losing its leaves.
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.