3. Agrostis gigantea Roth (redtop)
g–i; Map 525
A. stolonifera L. var. major (Gaudin) Farw.
Plants perennial, lacking stolons but with well‑developed
but often short rhizomes bearing more than 3 scales, forming loose tufts or
clumps. Flowering stems 30–100 cm long, erect to spreading, often ascending
from spreading bases. Leaf sheaths glabrous, the ligule 2–6 mm long, as long as
or longer than broad, rounded at the tip. Leaf blades 3–25 cm long, 2–8 mm
wide, flat or folded, glabrous or somewhat roughened, dark green to bluish
green. Inflorescences 8–25 cm long, open panicles, erect or somewhat nodding,
the main branches loosely ascending to spreading, branched again below the
middle, all or some with spikelets all of the way to the base, roughened.
Glumes 2.0–3.5 mm long. Lemma 1.4–2.5 mm long, narrowed to a bluntly or sharply
pointed tip, usually glabrous, awnless or with a slender straight awn, this
0.5–3.0 mm long, shorter than the spikelet. Palea relatively well developed,
1/2–2/3 as long as the lemma, 2‑nerved. Stamens 3, the anthers 0.8–1.5 mm
long. Fruits 1.0–1.4 mm long, reddish brown. 2n=42. June–August.
Introduced, scattered to common nearly throughout Missouri (native of Europe, cultivated and naturalized nearly throughout the U.S. and Canada). Bottomland forests, mesic upland forests, upland prairies, banks of streams,
spring branches, and rivers, margins of ponds and lakes, fens, alkaline seeps,
and moist ledges of bluffs; also pastures, old fields, ditches, levees, lawns,
roadsides, railroads, and moist, disturbed areas.
Steyermark (1963) included this species in his concept of A.
alba L., but Philipson (1937) and Widén (1971) determined that this name
was based upon material of a species of Poa. It is sometimes treated as
a variety of the closely related A. stolonifera, but the rhizomatous
habit and often longer, open inflorescences serve to separate it adequately
from that species. It is a component of some cool‑season grass seed mixes
for lawns and is also sometimes planted for erosion control. Steyermark (1963)
noted that it is an important cause of hay fever in June and July.