Sensitive Fern family (Onocleaceae)
Description: This native perennial fern consists of a few loose leaves that develop directly from the rootstock. The infertile leaves are 2-3' tall and erect or ascending, while the fertile leaves are 11½' tall and erect. The infertile leaves are light to medium green and ovate-lanceolate in overall shape; they are deeply pinnatifid for the most part, although their tips are more shallowly pinnatifid, while their bases are more pinnate. The central stalk (or rachis) of each infertile leaf is winged. The spreading narrow lobes of the infertile leaves are generously spaced from each other; their margins are undulate or shallowly pinnatifid and roll downward. Each infertile leaf has about 8 opposite pairs of these lobes. The basal stalks (or petioles) of the infertile leaves are about the same length or a little shorter than their blades; these stalks are dull yellow to reddish brown and glabrous or slightly chaffy. The infertile leaves persist all summer, but die down during the fall in response to frosts.
The fertile leaves have a very different appearance. Their leaflets form hard bead-like structures that enclose the sporangia and their spores. In overall shape, each fertile leaf is ellipsoid-oblongoid, forming an elongated panicle of bead-like leaflets on a long stout stalk. The fertile leaves become dark brown and persist through the winter. Eventually, their leaflets split open to release the spores. The root system consisting of a stout smooth rhizome with spreading fibrous roots. This rhizome occasionally branches. Occasionally, small vegetative colonies of plants are formed from the branching rhizomes.
Cultivation: The preference is partial sun to light shade, moist conditions, and soil that is loamy, silty, or sandy. Full sun is tolerated if the ground is consistently moist.
Range & Habitat: Sensitive Fern is fairly common and can be found in most areas of Illinois (see Distribution Map). It is native to eastern North America and East Asia. Habitats include moist to mesic deciduous woodlands, sandy savannas, bluffs, soggy thickets, forested bogs, swamps, moist meadows, moist sand prairies, edges of marshes, shady seeps and springs, and low shaded areas along ponds. The Sensitive Fern is usually found in natural areas of moderate to high quality.
Faunal Associations: The foliage is toxic to horses if it is eaten in quantity. The value of this fern to wildlife is low, although deer may eat the fronds to a limited extent.
Photographic Location: A wooded bluff in Vermillion County, Illinois. The fertile leaf in the lower photograph has persisted through the winter.
Comments: Fossil imprints have been found that closely resemble the Sensitive Fern; these imprints date back to the time of the dinosaurs. Thus, the Sensitive Fern appears to have changed very little during millions of years. The Sensitive Fern is the only member of its genus; its nearest living relative (in Illinois, anyway) is Matteuccia struthiopteris (Ostrich Fern), which looks very different. The Sensitive Fern can be readily distinguished from other ferns by its peculiar fertile leaves each fertile leaf resembles an elongated cluster of dark brown beads on a stalk. These fertile leaves are very persistent and can be observed near the infertile leaves throughout most of the year. The common name of this species refers to the deciduous nature of the infertile leaves and their sensitivity to frost; they do not coil back in response to being touched.