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ONOCLEA SENSIBILIS, Linnæus.
Sensitive Fern.
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.