Description: This native perennial fern consists of a single sterile leaf and a single fertile leaf that bears the spores; the latter is not always produced. The sterile leaf and fertile leaf (if present) are joined together at the base of their stalks; this typically occurs close to the ground. The blade of the sterile leaf is bipinnate-pinnatifid or tripinnate-pinnatifid in its structure; it spans up to 8" long and 8" across. This blade is divided into 1-3 major divisions; each division has a deltoid shape in outline, a bipinnate-pinnatifid structure, and a short stalk at its base.
Each major division of the sterile leaf
has up to 7 pairs of leaflets; the lower leaflets are stalked, while the upper
leaflets are sessile. The lower leaflets and some of the upper leaflets are
divided into up to 7 pairs of subleaflets that are oval to oblong-lanceolate in
shape; usually the terminal subleaflets are more elongated than the lateral
subleaflets. The subleaflets and undivided upper leaflets have finely serrated
or crenate margins; sometimes they are irregularly cleft into smaller lobes.
The sterile leaf blade is evergreen; it is medium green during the summer, but
becomes bronze-colored during the winter (hence the common name). The stalk of
the sterile blade is 3-8" long and slightly succulent; both the sterile blade
and its stalk are hairless. The fertile leaf blade has a very different
appearance from the sterile blade; this blade has a bipinnate or tripinnate
structure, but it is contracted into sporangia-bearing branches. The fertile
leaf blade is up to 10" tall and 5" across; it is initially light green, but
later becomes yellow or brown. The branches of
the fertile blade bear
dense rows of small globoid sporangia; during the fall or winter, the latter
split open to release their minute spores to the wind. The root system consists
of fibrous roots that are fleshy and shallow; occasionally, vegetative offsets
develop from spreading rhizomes.
Cultivation: This fern prefers semi-open areas with
dappled sunlight or partial shade; the soil should be well-drained. Because the
root system is partially dependent on mycorrhizal fungi in the soil, this fern
does not adapt to cultivation readily and it is unlikely to survive
transplantation from a natural area.
Range
& Habitat: The Bronze Fern is occasional throughout Illinois
(see
Distribution
Map). Habitats include open woodlands, upland savannas, areas along
woodland paths, grassy meadows, gravelly seeps, and pastures. This fern is
often found in thinly-wooded upland areas where Oak trees are
present.
Faunal Associations: The
Wild Turkey has been found to eat the fronds of Botrychium spp. (Grape
Ferns) to a limited extent; the Ruffed Grouse and White-Tailed Deer probably
eat the fronds as well.
Photographic
Location: The upper photograph of the sterile leaf was taken along a
path in an upland oak woodland in McLean County, Illinois. The lower photograph
of the fertile leaf was taken at Busey Woods in Urbana,
Illinois.
Comments: The Bronze Fern
has a very different appearance from the typical variety of this species,
Botrychium dissectum dissectum (Cutleaf Grape Fern); the latter has
conspicuous dentate margins and shorter terminal leaflets or subleaflets.
However, both varieties of this species become bronze during the winter. Other
similar Botrychium spp. (Grape Ferns) have sterile leaves that remain
green during the winter; they are less common and more restricted in their
distributions within the state. Another species, the common Botrychium
virginianum (Rattlesnake Fern), has deciduous sterile leaves that are
larger in size and divided into more numerous leaflets and subleaflets. An
alternative scientific name of the Bronze Fern is Botrychium
obliquum.