Festuca is circumscribed to include the annual species recognized in the Field Manual of Michigan Flora as Vulpia.
In many specimens the tip of the palea is narrow, ± inrolled, and projecting slightly beyond the tip of the lemma. A superficial glance at a pressed specimen may thus suggest a bifid tip to the lemma, when this is in fact not the case.
1. Blades of leaves flat (or merely once-folded), at least the larger ones (2.5–) 3–8 mm broad; lemmas awnless or rarely with awn less than 0.8 mm long.
2. Larger lemmas 2.5–4.5 mm long, glabrous to finely papillose; anthers 0.8–1.4 mm long; spikelets mostly containing 2–4 (–5) florets.
2. Larger lemmas 5.5–8 mm long, scabrous; anthers 2.2–3.5 (–3.8) mm long; spikelets often containing 5 or more florets.
F. altaica (in part)
1. Blades of leaves ± strongly involute, less (usually much less) than 3 mm broad; lemmas awned or awnless.
3. Plants annual, usually in small tufts or solitary; florets cleistogamous, with usually one included anther (rarely 3 anthers).
4. Lower (shorter) glumes more than half the length of the upper glumes.
4. Lower (shorter) glumes less than half the length of the upper glumes.
3. Plants perennial, usually in dense tufts including numerous dry sheaths of previous years; florets open at anthesis, with 3 anthers.
5. Second (larger) glume ca. 5.5–7.5 mm long; larger lemmas ca. 6–7.5 mm long, somewhat keeled, ± strongly scabrous over the back, merely acute or at most very short-awned; plants tall (ca. 5–8 dm) and stout, the blades of the lower leaves disarticulating from their stiff persistent sheaths.
F. altaica (in part)
5. Second glume less than 5 mm long; larger lemmas ca. 2.5–6.5 mm long, not at all keeled, scabrous to smooth or somewhat hairy, distinctly awned (except in F. filiformis); plants rather more slender and usually shorter than F. altaica, the lower sheaths persistent or not.
6. Lemmas awnless, ca. 2.5 (–3) mm long; leaves hair-like, at most 0.2 mm thick, mostly more than half as high as the culm.
6. Lemmas awned, the body ca. 3–6.5 mm long; leaves often stiff, up to 0.8 mm thick, and in some species mostly less than half as high as the culm.
7. Margins of lemmas conspicuously thin and membranous; summit of ovary bristly-pubescent; awns (at least the longer ones) more than 3 mm long, nearly equaling or longer than the bodies of their lemmas; mature panicle open and lax.
7. Margins of lemmas at most very narrowly membranous-bordered, the lemmas ± firm and thick throughout; summit of ovary glabrous; awns all less than 3 (–4) mm long, shorter than the bodies of their lemmas; mature panicle rather narrow, crowded, and compact, the branches strongly ascending or, if spreading, very short.
8. Sheaths closed in young leaves, the old ones ± dark reddish brown basally, becoming fibrous by splitting between the prominent pale veins; basal shoots usually arising laterally, the culms thus tending to be strongly curved or bent at the base; anthers (1.7–) 2.1–3.5 (–3.7) mm long.
8. Sheaths open most of their length even in young leaves (margins ± overlapping), the old ones mostly pale or drab brown, not becoming fibrous; basal shoots erect, the culms thus nearly or quite straight from the base upwards; anthers various.
9. Anthers (1.8–) 2–3 mm long; lower panicle branches often spreading.
9. Anthers 1–1.6 (–1.8) mm long; lower panicle branches strongly ascending.