Description: This adventive perennial grass is ½–1¼' tall and tufted at the base, consisting of fertile and infertile shoots. Fertile shoots have 2-4 alternate leaves along the lower-third of the culm, while infertile shoots have about 4 leaves that are sheathed together in the shape of a fan. The culms are pale green to tan, somewhat flattened, glabrous, and unbranched. The leaf blades of fertile shoots are about 2 mm. across and 3-4" long; they are light blue-gray to pale green, hairless, and ascending to spreading. The leaf blades of infertile shoots are the same as those of the fertile shoots, except they are often somewhat longer (up to 6½" in length). The leaf sheaths are light blue-gray to pale green, hairless, and membranous along their margins; they are often rather loosely attached to their culms. The ligule at the junction of each blade and sheath has a papery membrane and a few white hairs.
Each fertile shoot terminates in a large
inflorescence up to 5½" tall and 11" across. This inflorescence has
whorls or near-whorls of floral spikes along its central axis (or rachis). The
lower to middle whorls of spikes are widely spreading, while the upper spikes
are ascending and somewhat shorter in length. Each floral spike is up to
5½" long; small spikelets are evenly distributed along its length. Each
spikelet is about 4 mm. long (excluding the awns) and V-shaped at the base; it
has a pair of glumes, a fertile lemma, and an infertile lemma. One glume is
about 3 mm. long, while the other glume is about 4 mm. long; they are narrowly
lanceolate and keeled. The fertile lemma 2-3 mm. long, and folded along its
length; at the apex, it has an awn about 5-8 mm. long. The infertile lemma is
1.5–2 mm. long, folded along its length, and obtuse or truncate at its
apex, where there is an awn about 3-4 mm. long. In Illinois, the blooming
period occurs during the summer. The spikelets are initially reddish green, but
they later turn tan or brown when the grains become ripe. At this time, the
entire inflorescence may break off and tumble in the wind, thereby distributing
the grains. The root system is fibrous and rhizomatous; sometimes rootlets form
along the lower nodes of the culms. Where there is little competition from
other vegetation, this grass often forms vegetative colonies.
Cultivation: Preferred growing conditions are full
sun and dry barren soil containing gravel or sand. Because of its low growth
habit, this grass can adapt to a regimen of mowing.
Range & Habitat: Windmill Grass is still
uncommon in Illinois (see
Distribution
Map), although it is probably becoming more abundant, especially in sandy
areas of the state. This grass is native to the southern Great Plains and
grassy areas of the SW in the United States. Habitats include dry upland
prairies, dry sand prairies, gravelly areas along railroads and roadsides,
lawns, and barren waste areas.
Faunal
Associations: Little is known about the floral-faunal relationships
for this grass, particularly in Illinois and other Midwestern states, where it
is adventive. The foliage of Windmill Grass is eaten by the American Bison in
the southern Great Plains, and it is probably edible to other hoofed herbivores
as well. Various sparrows, Mourning Doves, and other granivorous birds may eat
the seeds, but this is speculation on my part.
Photographic Location: A gravelly area along a
railroad track in Champaign, Illinois. The upper photograph was taken directly
above the inflorescence.
Comments:
The inflorescence of this little grass has the shape of a windmill or
television antenna. Windmill Grass superficially resembles one of the more
common Digitaria spp. (Crabgrasses), but its inflorescence has more
vertical depth with 2-4 whorls of spikes along the central axis (or rachis).
The inflorescence of the typical Crabgrass is more digitate with a single whorl
(or near-whorl) of ascending spikes. Also, the spikelets of Windmill Grass have
awns, while those of Crabgrass are awnless. Another grass species, Chloris
gayana (Finger Grass), is adventive from Africa and quite rare in Illinois.
It is much taller (often exceeding 3' in length) and its inflorescence is more
digitate. Other Chloris spp. haven't been observed in Illinois; like
Windmill Grass, many of them are native to the southern Great Plains and grassy
areas of the desert SW. These latter species tend to be smaller in size than
Windmill Grass, and their spikelets have shorter awns (less than 4 mm.) or they
lack awns altogether.