Onoclea sensibilis:—Root-stock creeping, elongated; stalks scattered, nearly chaffless, a few inches to over a foot high; fronds dimorphous; sterile ones triangular-ovate, foliaceous, smooth, quickly withering when plucked, deeply pinnatifid into several oblong-lanceolate entire or sinuate or sinuately pinnatifid segments, the lowest pair sometimes distinct, the rest connected by a wing which widens upwards; the veins reticulated and forming narrow paracostal areoles, and, outside of these, copious oblong or hexagonal meshes; fertile fronds shorter, contracted, rigid, closely bipinnate; the pinnules rolled up into berry-like bodies; veins free, simple or forked, soriferous on the back; sporangia borne on an elevated receptacle, half surrounded by a very delicate somewhat hood-like indusium attached at the base of the receptacle.

Onoclea sensibilis, LinnÆus, Sp. Pl., p. 1517.—Michaux, Fl. Bor.-Am., ii., p. 272.—Swartz, Syn. Fil., p. 110.—Schkuhr, Krypt. Gew., p. 95, t. 102.—Willdenow, Sp. Pl., v., p. 287.—Pursh, Fl. Am. Sept., ii., p. 665.—Hooker, Gen. Fil., t. lxxxii; Fl. Bor.-Am., ii., p. 262; Sp. Fil., iii., p. 160.—Torrey, Fl. New York, ii., p. 499.—Gray, Manual, ed. i., p. 457; ed. ii., p. 599, t. xii; ed. v., p. 668, t. xviii; Botany of Japan, in Mem. Amer. Acad. (n. s.) vi., p. 421.—Mettenius, Fil. Hort. Lips., p. 97.—Maximowicz, Prim. Fl. Amur., p. 337.—Eaton, in Chapman’s Flora, p. 596.—Hooker & Baker, Syn. Fil., p. 46.—Miquel, Prolus. Fl. Jap., in Ann. Mus. Bot. Lugd.-Batav., iii., p. 179.—Milde, Fil. Eur. et Atlant., p. 157.—Redfield, in Bulletin of Torrey Botan. Club, vi., p. 4.—Williamson, Ferns of Kentucky, p. 109, t. xli; Fern-Etchings, t. xlv.

Onoclea obtusilobata, Schkuhr, Krypt. Gew., p. 95, t. 103.—Pursh, Fl. Am. Sept., ii., p. 665.

Onoclea obtusiloba, Link, Fil. Hort. Lips., p. 37.

Osmunda frondibus pinnatis foliolis superioribus basi coadunatis, omnibus lanceolatis, pinnato-sinuatis, LinnÆus, Hort. Cliff., p. 472.—Gronovius, Fl. Virginica, p. 196; ed. ii., p, 163.—(Other ancient names are repeated by LinnÆus and Willdenow.)

Hab.—Wet meadows and thickets, from New Brunswick to the Saskatchewan, extending southward through Dacotah, Kansas, and Arkansas to Louisiana, and eastward to St. Augustine, Florida, one of our commonest and most abundant ferns, often occupying large portions of land to the partial exclusion of other plants. Not found in western America or in Europe, but occurring in Japan, Mantchooria and eastern Siberia.

Description:—The root-stock is about one-third of an inch thick, and irregularly roundish in section. It creeps widely below the surface of the ground, rooting freely and often forking, so that in cultivation it is very difficult to confine the plant to one spot. The root-stock contains six or eight roundish or flattened fibro-vascular bundles arranged in a circle near the outer surface. It bears no chaff. The stalks are scattered along its length, the apex being covered with the thickened stalk-bases of next year’s fronds, and the stalks for the present year rising a few inches back of the apex.

The fronds are truly dimorphous, the fertile ones being so unlike the sterile, that no one who is unacquainted with the plant would suppose they had anything to do with each other.

The sterile fronds vary in length from one or two inches to fifteen or eighteen, and are supported on stalks usually rather longer still, so that, while the smallest plants may be concealed in the grass, the tallest ones are often fully three feet high. The bases of the stalks are flattened, discolored and very sparingly chaffy; the upper part is green in the living plant, brownish-stramineous when dried, smooth and naked, rounded at the back, and slightly furrowed in front. It contains two obliquely-placed strap-shaped fibro-vascular bundles, which unite below the base of the frond and form one having a U-shaped section. The outline of the sterile fronds is triangular or triangular-ovate. The midrib is winged, either from the very base, or from the second pair of segments; the wing at its lower extremity very narrow, but gradually widening towards the apex, so that its greatest width is but little less than that of the terminal segment. The number of segments in the smallest fronds is two or three on each side; in the largest fronds twelve or thirteen on each side. The lowest segments are rather more than half as long as the whole frond; the next segments usually a little smaller, but sometimes a little longer than the first pair, and the remaining ones rapidly decreasing. The segments are broadly lanceolate or oblong-lanceolate, narrowed at the base, especially the lower ones, and either rounded or sub-acute at the apex. The sinuses between them are rounded, and are gradually narrowed towards the apex of the frond. The segments are very minutely serrulate on the edges; the smallest ones otherwise entire, and the larger ones either with sinuous margins or, in large fronds, deeply sinuous-pinnatifid. The texture is herbaceous, the surfaces perfectly smooth, the color of the upper surface grass-green, of the lower surface paler and slightly glaucescent. The fronds wilt very soon after plucking them, and in wilting there is a slight disposition to fold the segments together, face to face, for which reason the plant has received the name of “Sensitive-Fern.” The first frost of autumn destroys the sterile fronds; and a late frost in May or June does the same. The midribs are prominent, and the veins conspicuous; the latter being copiously reticulated into areoles which enclose no free veinlets. Along the sides of the midribs and midveins are very long and narrow areoles, and outside of these are obliquely-placed oblong areoles in several irregular rows.

The fertile fronds are not very common, and a young botanist may search in vain for them for a long time. They stand only about half as high as the sterile fronds, and are very rigid. They are nearly black in color: in winter they dry up, but remain erect through the next summer, so that a fruiting plant often has fertile fronds standing of two years’ growth. The frond is only a few (usually four to six) inches long, and consists of from four to ten pairs of appressed fleshy or cartilaginous pinnÆ, which are divided into a double row of sub-globose bead-like segments or pinnules; the whole looking like a small and narrow but dense cluster of diminutive grapes. Each pinnule has its edges so much recurved that the whole forms a sort of pouch, apparently filled with sporangia.

Mr. Faxon has made a careful study of the sori, and has very kindly furnished the account given below.[5]

The articulations of the sporangia are said by FÉe to be twenty-eight to thirty-two, and more numerous than in any other fern. I have counted only thirty at most, and more frequently only twenty-eight. The spores are ovoid and very dark-colored.

Var. obtusilobata, Torrey, Fl. New York, ii., p. 499, t. clx (Onoclea obtusilobata, Schkuhr), is not a permanent variation of the species, but is based on a not infrequent condition of the plant, in which the pinnÆ of some of the foliaceous fronds become deeply pinnatifid into obovate segments, which have mostly free veins and imperfectly developed sori. The indusia appear as little whitish scales on the back of the veins. It occurs in almost all places where the plant is common, is often produced from root-stocks which bear also normal fronds, and presents all gradations from the usual sterile frond to the proper fertile one. Ragiopteris onocleoides of Presl is founded on a young fertile frond of this species placed with a sterile one of what Milde judges to be a monstrous form of Aspidium Filix-mas. Maximowicz describes a var. interrupta, from the Amoor region, in which the fertile frond nearly equals the sterile, and has elongated pinnÆ, with remote segments. This condition is also sometimes seen in American specimens, and is hardly a true variety.

In an article on “The late Extinct Floras of North America,” which appeared in Vol. ix of the Annals of the New York Lyceum of Natural History, in April, 1868, Professor Newberry describes certain fossil specimens of ferns occurring in Miocene argillaceous limestone at Fort Union, Dacotah, and refers them with little hesitation to this species. I have not seen the specimens, but, as similar venation and not very dissimilar fronds are seen in Woodwardia and Pteris, one may perhaps doubt the absolute certainty of the identification.