OregonFlora: Festuca idahoensis

	Festuca idahoensis
	Idaho fescue
Habit	Plants 30–100 cm tall; densely cespitose, glaucous or less often green.
Culms	basal branching intravaginal.
Leaves	mostly basal; sheaths open, glabrous to hairy, usually pale (white, pink, light brown) and lacking contrasting veins, crumbling or somewhat splitting between the veins but not shredding; blades readily spinning between the fingers; collars glabrous; ligules 0.3–0.6 mm; blades (5)8– 25(35)cm × 0.3–1 mm as folded, conduplicate, usually glaucous, sometimes green; outer surface scabrous, sometimes with long hairs; inner surface with hairs about as long as the leaf is thick; flag leaves (1.5)3–7(9.5) cm, usually conduplicate, sometimes loosely rolled.
Inflorescence	s (5)7– 12(20) cm; open at anthesis; lowest node with 1–2 branches; branches (5.8)7.5–17(19)mm, ascending to reflexed at anthesis, appressed after anthesis or the lower branches sometimes remaining spreading to reflexed.
Spikelets	(5.8)7.5–17(19)mm, with (2)3–7(9) florets.
Glumes	glabrous or hairy at the tips only; lower glumes (2.5)3–5(6)mm, 1–3-veined; upper glumes (3)4–8 mm, 3–4-veined.
Caryopses	4–4.5 mm, glabrous.
Ovaries	apex glabrous.
Leaf anatomy	cross sections 0.35–0.6 × 0.55– 0.7 mm; more or less round or hexagonal; veins (4)5(6); ribs (1)3(5); dorsal sclerenchyma in broad bands more than twice as wide as thick, occasionally continuous.
Lemma	(5.8)6–8(10)mm, 0(1)-veined; hairs on the distal part only; lemma awns (1)2–6(7) mm; shorter than to occasionally equaling the lemma body.
Anthers	(2.5)3.2–4(4.5) mm.
2n	=28.

	Festuca idahoensis
Distribution	[WildflowerSearch map] [BONAP county map]
Discussion	Prairie, grassland, shrub-steppe, open pine forest, often in partial shade or on north-facing slopes; also on south-facing slopes in subalpine and alpine zones. 100–3000 m. BR, BW, Casc, Col, ECas, Lava, Owy. CA, ID, NV, WA; north to British Columbia, northeast to Saskatchewan, SD, and NM. Native. Festuca idahoensis is the most common fine-leaved fescue east of the Cascades. However, very similar fescues have been introduced. Festuca trachyphylla and F. valesiaca, planted on roadsides and used to renovate dry pastures, have shorter lemmas and denser inflorescences. Robust individuals of F. occidentalis can be similar to F. idahoensis, but in F. occidentalis many of the lemma awns are longer than the lemmas. In alpine sites, F. idahoensis can be confused with F. brachyphylla and F. saximontana, which have shorter lemmas. Plants west of the crest of the Cascades that were once included in F. idahoensis are now recognized as a distinct species, F. roemeri, which has broader leaves than F. idahoensis.
Source	Flora of Oregon, volume 1, page 410 Barbara Wilson, Richard Brainerd, Nick Otting
Sibling taxa	F. brachyphylla, F. californica, F. campestris, F. elmeri, F. filiformis, F. lemanii, F. occidentalis, F. roemeri, F. rubra, F. saximontana, F. subulata, F. subuliflora, F. trachyphylla, F. valesiaca, F. viridula
Synonyms	Festuca idahoensis var. idahoensis, Festuca idahoensis var. oregona
Web links	Local floras: BC, CA, OR, WA Local Web sites: CalFlora, CalPhotos, Flora NW, PNW Herbaria WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search

Festuca idahoensis

Idaho fescue

Habit

Plants 30–100 cm tall; densely cespitose, glaucous or less often green.

Culms

basal branching intravaginal.

Leaves

mostly basal;

sheaths open, glabrous to hairy, usually pale (white, pink, light brown) and lacking contrasting veins, crumbling or somewhat splitting between the veins but not shredding;

blades readily spinning between the fingers;

collars glabrous;

ligules 0.3–0.6 mm;

blades (5)8– 25(35)cm × 0.3–1 mm as folded, conduplicate, usually glaucous, sometimes green;

outer surface scabrous, sometimes with long hairs;

inner surface with hairs about as long as the leaf is thick; flag leaves (1.5)3–7(9.5) cm, usually conduplicate, sometimes loosely rolled.

Inflorescence

s (5)7– 12(20) cm; open at anthesis; lowest node with 1–2 branches;

branches (5.8)7.5–17(19)mm, ascending to reflexed at anthesis, appressed after anthesis or the lower branches sometimes remaining spreading to reflexed.

Spikelets

(5.8)7.5–17(19)mm, with (2)3–7(9) florets.

Glumes

glabrous or hairy at the tips only;

lower glumes (2.5)3–5(6)mm, 1–3-veined;

upper glumes (3)4–8 mm, 3–4-veined.

Caryopses

4–4.5 mm, glabrous.

Ovaries

apex glabrous.

Leaf anatomy

cross sections 0.35–0.6 × 0.55– 0.7 mm; more or less round or hexagonal;

veins (4)5(6);

ribs (1)3(5); dorsal sclerenchyma in broad bands more than twice as wide as thick, occasionally continuous.

Lemma

(5.8)6–8(10)mm, 0(1)-veined;

hairs on the distal part only;

lemma awns (1)2–6(7) mm; shorter than to occasionally equaling the lemma body.

Anthers

(2.5)3.2–4(4.5) mm.

=28.

Festuca idahoensis

Distribution

[WildflowerSearch map]

[BONAP county map]

Discussion

Prairie, grassland, shrub-steppe, open pine forest, often in partial shade or on north-facing slopes; also on south-facing slopes in subalpine and alpine zones. 100–3000 m. BR, BW, Casc, Col, ECas, Lava, Owy. CA, ID, NV, WA; north to British Columbia, northeast to Saskatchewan, SD, and NM. Native.

Festuca idahoensis is the most common fine-leaved fescue east of the Cascades. However, very similar fescues have been introduced. Festuca trachyphylla and F. valesiaca, planted on roadsides and used to renovate dry pastures, have shorter lemmas and denser inflorescences. Robust individuals of F. occidentalis can be similar to F. idahoensis, but in F. occidentalis many of the lemma awns are longer than the lemmas. In alpine sites, F. idahoensis can be confused with F. brachyphylla and F. saximontana, which have shorter lemmas. Plants west of the crest of the Cascades that were once included in F. idahoensis are now recognized as a distinct species, F. roemeri, which has broader leaves than F. idahoensis.