Smooth cliff brake is a perennial fern that grows as a cluster of leaves from a rhizome. It typically grows out of an exposed limestone or dolomite bluff or rock.
The stiff, wiry stems are brown, hairless, or with a few scattered hairs.
In general outline, the entire leaf (frond) is narrow, lance-shaped or oblong, and is once- or twice-compound.
The leaflets can be leathery or not and sometimes have 1 or 2 lobes at the base. Leaflets are narrowly lanceolate to ovate or oblong, lacking hairs.
Spores are borne on the undersides of the leaflets, in a continuous band along the outer margin, protected by the recurved edge of the leaflet.
Spores are produced April–October.
Similar species: Missouri has only one other species in this genus:
- Purple cliff brake (P. atropurpurea) has fronds that take two different forms; Fertile fronds have spore-bearing leaflets, which are narrower and more divided, while the sterile fronds have leaflets that are wider and more rounded. Also, the stems and midveins of purple cliff brake are densely hairy with short, curly hairs on the upper surface. It can be a larger plant: its leaves can be 20 inches long, and its leaflets can be 1½ inches in length. Also, it is more likely to grow in soil and is not as limited to cliff-face habitats.
- See Life Cycle for information about two virtually identical varieties of smooth cliff brake that occur in Missouri.
Leaf length: 3 to 9 inches; leaflet length: ¼ to 1 inch.
Scattered throughout the Ozark and Ozark Border regions, and also occurs north, locally, to Andrew, Knox, and Lewis counties.
Habitat and Conservation
Occurs on crevices and ledges of limestone and dolomite bluffs, boulders, and rock outcrops, rarely on sandstone.
Compared to the similar purple cliff brake, this fern is more strongly limited to exposed, rocky habitats and is less likely to be seen growing in soil.
Status
Native Missouri fern.
Life Cycle
Ferns have a two-part life cycle. The plants we usually see are called sporophytes, because they produce spores that germinate and become the other part of the life cycle, the gametophytes.
Gametophytes in this family of ferns are small, green, flat, kidney- or heart-shaped plants that few people notice. The gametophytes produce eggs and sperm, which unite to become a new sporophyte plant.
Cliff brake species, however, are famous for hybridizing with each other, and for creating offspring that are polyploid (possess more than two sets of genetic information in each cell), and for reproducing via apogamy. Apogamy is when a new sporophyte plant forms without fertilization — so it has the same number of genetic copies as the gametophyte.
Missouri has two varieties of smooth cliff brake; to the naked eye, they look alike. They can only be distinguished by looking at the spores under a microscope:
- Var. glabella reproduces via apogamy and has larger spores (it is tetraploid, possessing 4 sets of each gene); it is more common.
- Var. missouriensis reproduces sexually and has smaller spores (it is diploid, possessing 2 sets of each gene); it’s the ancestor of var. glabella and is limited to only a few counties.
Human Connections
Why is it “brake” and not “break”? It is logical to think of these cliff-loving ferns as plants that ultimately help “break apart” the rock surfaces of bluffs, but the word brake, with Middle English and Scandinavian roots, actually means “fern.” This is why we don’t call these plants “cliff brake ferns.” For the same reason, there is a fern called “bracken” and not “bracken fern.”
The genus name, Pellaea, is from a Greek word for "dark," in reference to the brownish or blackish stems typical in this genus. The species name, glabella, means "glabrous" (smooth; hairless) and refers to the mostly hairless leaf stems.
Ecosystem Connections
Little information is available about the connections between smooth cliff brake and insects and other animals. As enduring plants of cliff, bluff, and other dry, rocky habitats, cliff brake surely provides cover for insects and spiders that live in those natural communities. And small birds can perch on these ferns to forage for the insects and spiders!
Also, like other vegetation that grows in rock crevices, these ferns contribute to the weathering of rock faces.
Apogamy, common in this fern family, is where new sporophyte plants develop without sexual reproduction, basically skipping the gametophyte stage. This adaptation, allowing them to reproduce without water, helps ferns that live in dry environments, since sperm require water to swim to eggs for fertilization.
