Description: This native sedge is a summer annual up to
12" tall. It is unbranched, except at the base, where it sends up many culms
that are erect or sprawling. Each culm is up to 10" long, medium green,
3-angled, and glabrous, becoming brownish at the base. During the blooming
period, there are 1-2 alternate leaves along each culm. Each leaf is up to 4"
long, 1/8" across, medium green, narrowly linear, and glabrous. The leaves are
often folded upward along their central veins. The withered remains of older
leaves may persist at the base of each culm. Each culm terminates in an
inflorescence consisting of one or more flowering spikes. Some spikes may be
sessile, while others have short stalks up to 2" long. At the base of the
inflorescence, there are 2-4 leafy bracts up to 4" long. These bracts resemble
the leaves and spread outward. Each spike consists of 3-7 flattened spikelets
with smooth margins, while each spikelet consists of 8-18 flowers. The scales
of these flowers are arranged in 2 columnar ranks within the spikelet; they are
flattened and closely appressed together. Each spikelet is about 1/3" long and
oblongoid in shape; its floral scales are shiny purplish or reddish brown,
except at the margins, where they are pale green or yellow. In addition to its
floral scale, each flower has a bipartite deciduous style and 2-3 stamens. The
styles of the flowers are enclosed by the scales, or they are barely exerted
(less than 2 mm. beyond the scales). The blooming period occurs from mid-summer
to early fall. The flowers are wind-pollinated. Each flower produces a single
achene that is somewhat flattened and pointed at one end. The root system
consists of a tuft of fibrous roots. This sedge often forms dense colonies
along bodies of water.
Cultivation:
The preference is full or partial sun and wet to moist conditions. Various
kinds of soil are tolerated, including those that are sandy, gravelly, shallow
and rocky, and muddy. This sedge tolerates occasional flooding.
Range & Habitat: Shining Flat Sedge occurs
occasionally in central and northern Illinois, while in the southern part of
the state it is uncommon. Habitats include sedge meadows, seeps, swamps, and
low-lying areas along streams and lakes, including sand bars, gravel bars, and
muddy islands. This sedge can be found in either degraded or higher quality
wetlands.
Faunal Associations: The
caterpillars of Glyphipterix impigritella (Flat Sedge Borer Moth) bore
into the stems of Cyperus spp. (Flat Sedges). The seeds of Flat Sedges
are eaten to a limited extent by some wetland birds, including the Green-Winged
Teal, Bobolink, and Wilson Snipe. The Canada Goose also eats the
foliage.
Photographic Location:
Along the border of a lake at Kaufman Park in Champaign,
Illinois.
Comments: The spikelets of
Shining Flat Sedge are rather unusual and attractive. When this sedge is not in
bloom, it superficially resembles an Eleocharis sp. (Spike Rush) because
of its narrow leaves and culms. However, the leaves and culms of Shining Flat
Sedge are often joined together at the base to form tufts, while the culms of a
typical Spike Rush poke out of the ground individually. Shining Flat Sedge can
be distinguished from most other Cyperus spp. (Flat Sedges) by its
colorful spikelets, which are primarily purplish or reddish brown, even at an
early stage of development. Another species that occurs in Illinois, Cyperus
diandrus, has similar spikelets and foliage. This latter species produces
persistent styles that are exerted from the floral scales by as much as 4 mm.,
while the styles of Shining Flat Sedge are less exerted and conspicuous.
Sometimes Shining Flat Sedge is referred to as Cyperus rivularis,
however this scientific name is considered obsolete. Mohlenbrock (1976/2001)
describes different forms of this species that occur in Illinois. The typical
form, f. bipartitus, which is described here, is less than 12" tall and
has purplish or reddish brown floral scales. This is by far the most common
form of Shining Flat Sedge in Illinois. Another form, f. elongatus, has
similar floral scales, but individual plants exceed 12" in length. The
remaining form, f. elutus, has floral scales that are straw-colored;
otherwise, it is identical to the typical form.