Sensitive fern is a rather pushy plant, spreading unabashedly to form a lush groundcover of triangular, bright green fronds that shelter salamanders and frogs in moist, shaded areas such as swamps, marshes, and stream banks. The Ohio Department of Natural Resources classifies sensitive fern as a facultative wetland plant, which means it usually occurs in wetlands or soggy grounds at the edge of water in shade or sun but is occasionally found in non-wetlands. It can grow four feet tall in wet shade, although the typical height is half that size. Sensitive fern has several distinctive features that set it apart from other ferns. The rachis (stem) of the sterile fronds is winged, or enclosed in a leafy edging, and the leathery, widely spaced, pinnately divided leaves are sub-divided into leaflets that display a network of veins that is unusual in the fern world. The fern's common name derives from the plant's extreme sensitivity to cold; the fronds turn black at the slightest touch of frost. The upright fertile fronds have an entirely different appearance, with tightly contracted leaves and bead-like, spore-containing structures that turn brown during the summer (another common name is bead fern). If not eaten by birds or harvested for floral arrangements, the woody stalk and clusters of beads persist through winter to release spores in the spring. Sensitive fern also spreads through rhizomes to form colonies and is often the first plant species to inhabit disturbed areas. This adaptable fern is suitable for both rain and drought gardens because it tolerates occasionally dry soils in shade. Give it room to spread or plant it next to growers that can hold their own. Suitable companion plants include dogwoods, common ninebark, snowberry, viburnums, spotted Joe-pye weed, spiderwort, and red milkweed. Sensitive fern's thick, wavy-edged leaves contrast nicely with the delicate, lacy fronds of other fern species. 
 
Sensitive fern’s native range is the north, central, and eastern regions of the US, and it’s common throughout Ohio. Onoclea comes from the Greek words onos, meaning “a vessel,” and kleio, meaning “to close,” referring to the rolled-over edges on the sori (see description of leaves below). Some experts consider sensitive fern to be the only species in the genus Onoclea. The species name translates to “sensitive.”  The modern-day sensitive fern is virtually identical to a fossil from 57 million years ago.
 
According to ecologist Mary F. Wilson, The Juneau Empire (2020), not as many wildlife species feed on ferns as compared to flowering plants and conifers. Instead of the usual suspects (beetles, moths, and butterflies), species of sawflies and two taxa of true bugs (such as aphids) are typically found sucking on the plant juices of ferns. In the case of sensitive fern, three moths are also known to feed on the stems and rhizomes: olive angled shades, silver-spotted fern, and sensitive fern borer.
 
Native habitats include freshwater areas, swamps, wet meadows, thickets and bogs, roadside ditches, and banks of streams and rivers. Useful for massing in rain gardens and ditches. Plant along woodland borders, as a groundcover, and along water features. Cut fertile fronds are valued for floral arrangements.
 
Plant Characteristics:
Grows 1-4’ tall and wide.
 
Prefers part or full shade; tolerates full sun with consistent moisture. Tolerant of occasional drought or dry soils.
 
Prefers acidic, sandy, or loamy soils; does well in moist, average soils, including clay. Tolerates extremely wet soils or drier conditions in shade.
 
Sterile fronds are yellow green to pale green, triangular, and deeply cut into 8-12 pairs of nearly opposite pinnae that have prominent netted veins and wavy edges. Twice-pinnate fertile fronds are green and 10-20” tall with steeply ascending, contracted pinnae (leaflets). The sori are at the tip of the stalk in bead-like bodies that mature from green to dark brown. They persist through winter and release green spores in the spring before the sterile fronds unfurl. The rolled-over edge of the pinna serves as an indusium, or cover, for the sorus. Spring fiddleheads are pale red with fine, whitish hair. Fall color is yellow or russet.
 
Stout, smooth rhizome has spreading fibrous roots. The rhizome occasionally branches and forms clonal colonies of plants.
 
Wildlife Value:
Host plant for 3 moth species (silver-spotted and olive angle shades moths pictured here) and the larvae of fern aphids, miners, and sawflies; fungi; bacteria; and scaldweed (Cuscuta gronovii), a parasitic vine that can overgrow and constrict the fern.
 
Medicinal, Edible, and Other Uses:
The Iroquois used an infusion of the root to help with childbirth, menstrual pain, and early stages of tuberculosis. A decoction was used to help with arthritis and infections.
 
The Iroquois reportedly cooked and ate the fiddleheads as an early springtime vegetable (cooking eliminates the fern’s thiaminase content).
 
Caution: The plant is poisonous to horses, especially in large amounts. The suspected cause is thiaminase poisoning, which causes an extreme vitamin B1 deficiency. Human toxicity is uncertain, but ferns may contain toxic substances in addition to thiaminase.