Description: This native perennial plant is about
2½–4' tall, unbranched, and more or less erect; vegetative clumps
of plants are often formed. The culm is green and glabrous. The alternate
leaves are up to 1½' long and ¾" across; there are up to 8 leaves
per culm. The leaf blades are yellowish green to dark green, linear in shape,
flat, glabrous, rough along the margins, and somewhat floppy. Venation of the
leaf blades is parallel; on some leaves, there are observable cross-veins
connecting the parallel veins at short intervals along the
blade (septate). The sheaths are glabrous
and septate as well. The culm terminates in an inflorescence consisting in a
compound umbel (less often, a simple umbel is produced); there are 3 or more
spreading leafy bracts underneath this umbel. The leafy bracts have the same
characteristics as the leaf blades; they are up to 1' long and ½"
across. The bracts are variable in size, but at least one of them is longer
than the inflorescence. A typical compound umbel produces several branches
(often called 'rays') in all directions; these branches are variable in length,
but can be several inches long. Each of these branches terminates in a small
cluster of 6-26 spikelets, from which short branchlets radiate in all
directions to terminate into additional clusters of spikelets. In some plants,
secondary branchlets develop to form even smaller clusters of spikelets. Both
the branches and branchlets of the compound umbel are stiff and straight. On
most plants, the spikelet clusters are arranged into irregular umbellets; they
are often somewhat compressed together. At the base of each umbellet, there are
one or more slender leafy bractlets; these bractlets are much smaller than the
leafy bracts at the base of the compound umbel. Each spikelet is about 3-6 mm.
(1/8–1/4") in length; it is greenish brown to blackish brown and ovoid,
consisting of numerous flowers with overlapping scales. These flowers have 3
stamens and a tripartite style. The outer scale of each flower is ovate, some
shade of brown, and about 1.5–2 mm. in length (less than 1/8"). The
blooming period occurs during early to mid-summer. Pollination is by wind. Each
flower is replaced by a tiny achene about 1.0 mm. long; this achene is
surrounded by 6 bristles that are about the same length as the achene. The
ripened achenes are 3-angled and light brown. The root system consists of
rhizomes and fibrous roots.
Cultivation: The preference is full to partial sun
and wet to moist conditions. This plant tolerates many kinds of soil, including
those containing clay, gravel, sand, or abundant organic material. The leaves
will become yellowish green if the soil dries out.
Range & Habitat: Dark Green Bulrush is a common
plant that occurs in every county of Illinois (see
Distribution
Map). Habitats include wet prairies, wet clay prairies, wet sand prairies,
wet dolomite prairies, sloughs in drier prairies, openings in floodplain
forests, marshes, sedge meadows, seeps, edges of ponds and rivers, and drainage
ditches. This plant can adapt to degraded wetland habitats.
Faunal
Associations: The caterpillars of Archanara oblonga (Oblong
Sedge Borer Moth) and Archanara subflava (Subflava Sedge Borer Moth)
bore through the culms of Scirpus spp. (Bulrushes). The seeds of
Bulrushes are eaten by numerous species of ducks and other birds (see the
Bird Table for a listing
of these species). The importance of the seeds as a food source varies with the
species of Bulrush and its abundance. The Canada Goose and Trumpeter Swan also
feed on the foliage of Bulrushes. Among mammalian herbivores, muskrats eat the
rootstocks and culms, while the Meadow Mouse occasionally eats the
seeds.
Photographic Location: A
roadside ditch in Jasper County, Illinois.
Comments: The Bulrushes (Scirpus spp.)
comprise a diverse group of plants in North America. Notwithstanding their
common name, Bulrushes are members of the Sedge family (Cyperaceae), rather
than Rushes (Juncaceae). Recently, there has been a taxonomic revision of the
Bulrushes. Dark Green Bulrush is a member of the Scirpus section and the
scientific names of Bulrushes in this group remain unchanged. Other Bulrushes
in the Scirpus section include Scirpus georgianus, Scirpus
hattorianus, Scirpus polyphyllus, and Scirpus microcarpus.
These latter species are uncommon in Illinois, and they are difficult to
distinguish from each other. The species Scirpus georgianus has 0-3
bristles surrounding its achenes and its spikelets are oblongoid in shape; Dark
Green Bulrush normally has 6 bristles and its spikelets are more ovoid in
shape. The species Scirpus hattorianus has leaves and bracts that lack
cross-venation and its bristles are shorter than the achene; Dark Green Bulrush
has septate foliage and its bristles are about the same length as the achene.
The species Scirpus polyphyllus has 10 or more leaves along its culms;
Dark Green Bulrush has 8 leaves or less per culm. The species Scirpus
microcarpus has sheaths that are reddish at the base and 4 bristles
surrounding its achenes; Dark Green Bulrush has green sheaths and 6 bristles
surrounding its achenes.