A perennial fern growing as a cluster of leaves from a rhizome, smooth cliff brake is almost always seen growing 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 is narrow, lance-shaped or oblong, and is once- or twice-compound. 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 in a continuous band along the outer margin, protected by the recurved edge of the leaflet. Spores are produced April–October.
Similar species: Purple cliff brake (P. atropurpurea) has somewhat dimorphic leaves (two different shapes, with the spore-bearing leaflets thinner and more divided, and the sterile leaflets wider and more rounded). Also, its stems and midveins 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.
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.
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 brakes, 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: var. glabella reproduces apogamously 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. You can only tell these two varieties apart by using a microscope!
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.”
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.