Description: This native
perennial grass is 3-8' tall, more or less erect, and unbranched or little
branched. Each culm is terete, tan, and hairless; its nodes are dark-colored,
slightly swollen, and glaucous. There are several alternate leaves that become
smaller as they ascend the culm. The leaf blades are up to 1½' long and
½" across; they are dull green to glaucous blue, linear in shape, mostly
hairless, and rather floppy. The leaf sheaths wrap tightly around the culms;
they are dull green to glaucous blue, and mostly hairless. Sometimes there are
short hairs near the ligules. Each culm terminates in 2-6 narrow racemes of
spikelets. These racemes originate near the base of the inflorescence and
spread outward, forming a claw-like V-shape. Each raceme is up to 6" long. The
spikelets occur in pairs along the raceme; they are appressed against the
central axis of each raceme, or they are slightly spreading. One spikelet in a
pair is sessile and perfect, while the other spikelet is pedicellate and
staminate. The pedicels of the latter spikelets are covered with short fine
hairs. Both kinds of spikelets are up to 1/3" (10 mm.) in length and similar in
size; they have narrowly lanceolate glumes. The fertile lemma of the sessile
spikelet has a straight awn up to ½" long. The spikelets are dull
greyish green to purplish red in color; their anthers are yellow to dull red.
The blooming period occurs during late summer or early fall. Pollination is by
wind. Each spikelet produces a single grain. The root system is fibrous and
produces short rhizomes. Big Bluestem is a bunchgrass as tight tufts of culms
are produced from these rhizomes.
Cultivation: The preference is full sun, moist to
slightly dry conditions, and a fertile loam or clay-loam. Other kinds of soil
are tolerated, including those containing sand and gravel. This is an easy
grass to grow, although it can be aggressive because of its large size. During
the winter, the naked culms have a tendency to flop over.
Range
& Habitat: Big Bluestem is a common grass that has been found in
every county of Illinois (see
Distribution
Map). Before the prairies covering much of the state were plowed under, Big
Bluestem covered large areas because it is one of the dominant species of the
tallgrass prairie. Habitats include black soil prairies, clay prairies, gravel
prairies, dolomite prairies, sand prairies, hill prairies, savannas, sandy
savannas, grassy fens,
limestone and sandstone glades, roadsides, and fallow fields. Big Bluestem is
often used in prairie restorations and it is occasionally used as an ornamental
grass in horticulture. It tolerates occasional wildfires, but not heavy
grazing.
Faunal Associations: The
caterpillars of several skippers feed on the foliage, including Atrytone
logan (Delaware Skipper), Atrytonopsis hianna (Dusted Skipper),
Hesperia leonardus (Leonard's Skipper), Hesperia metea (Cobweb
Skipper), Hesperia ottoe (Ottoe Skipper), Hesperia sassacus
(Indian Skipper), and Problema byssus (Byssus Skipper). Several
oligolectic species of leafhoppers feed on Big Bluestem and other Andropogon
spp. (Broom Sedges). The seeds are eaten sparingly by granivorous
songbirds, including the Field Sparrow, Tree Sparrow, and Chipping Sparrow. The
foliage is readily eaten by hoofed mammalian herbivores, including bison, deer,
cattle, and other livestock. The Meadow Vole and probably the Prairie Vole eat
the foliage as well.
Photographic
Location: The campus of the University of Illinois at
Urbana-Champaign.
Comments: This is
the dominant grass of the tallgrass prairie. Big Bluestem is a warm-season
grass with a C4 metabolism. As a result, it develops slowly during the cool
weather of spring and doesn't become tall until mid-summer. This provides an
opportunity for cool-season grasses and forbs to develop and produce flowers
before the Big Bluestem becomes dominant. The common name refers to the size of
this grass and the color of its leaves (both sheaths and blades). While some
specimens of Big Bluestem have blue leaves, others have dull green leaves.
Other Andropogon spp. (Broom Sedges) are shorter grasses that have
hairier spikelets. Usually, their pedicellate spikelets are much smaller than
their sessile spikelets, or they are undeveloped.