Plants perennial, forming tufts. Flowering stems 20–70 cm
long, erect, sometimes from spreading bases, glabrous, usually darkened at the
nodes. Leaf sheaths rounded on the back, glabrous or hairy, especially at the
tip, the ligule 1–4 mm long, often with an irregularly toothed or cut margin. Leaf
blades 2–30 cm long, 2–6 mm wide, flat, glabrous or hairy. Inflorescences 3–9
cm long, appearing as dense, cylindrical spikes, the branches very short and
mostly inconspicuous, but not fused to the main axis (sometimes the lowermost
branch more distinct and the inflorescence then interrupted at the base).
Spikelets 7–9 mm long (excluding the awns), slightly flattened laterally,
disarticulating above the glumes, with 3 florets, the uppermost perfect and the
lower 2 sterile. Glumes ovate, tapered to a sharply pointed tip, 3‑nerved
and somewhat keeled, awnless or nearly so, not winged along the midnerve,
roughened along the midnerve or hairy, longer than the lemmas, the lower glume
3.0–4.2 mm long, about 1/2 as long as the upper one, which is 7–9 mm long. Sterile
lemmas similar in size and shape, 3.0–3.5 mm long, longer than the fertile
floret, oblong‑elliptic, narrowed to 2 small teeth at the tip, densely
pubescent with orange or yellow hairs, the lowermost with a straight or
slightly curved awn 3–5 mm long attached toward the tip, the uppermost with a
sharply bent or twisted awn 6–9 mm long attached toward the base. Fertile lemma
1.8–2.1 mm long, broadly elliptic‑ovate, membranous and rounded at the
tip, but becoming thicker, brown, and shiny at maturity, wrapped tightly around
the palea and fruit and appearing sharply pointed. Palea of the fertile floret
slightly shorter and narrower than the lemma. Stamens 2, the anthers 3.2–4.5 mm
long. Fruits 1.4–1.6 mm long, oblong‑elliptic in outline, reddish brown.
2n=10, 20. May–August.
Introduced, uncommon and widely scattered in the state
(native of Europe, Asia; naturalized widely but sporadically nearly worldwide).
Pastures, lawns, railroads, and disturbed, open areas.
Crushed or newly mowed herbage of this species has a sweet
odor, caused by coumarins in the tissues. In some parts of its range, it is an
important cause of hay fever.
The closely related A. aristatum Boiss. eventually
may be found in Missouri. This native of Europe has become established
sporadically in the eastern United States, including Illinois, Iowa, and Arkansas. It differs from A. odoratum in its annual habit and in having
the awns of both sterile lemmas sharply bent or twisted.