Prairie Grasses: How to Identify a Grass

The following key contains a series of two or more contrasting statements. Compare the characteristics of the grass you want to identify with the distinguishing feature(s) mentioned in the statements. If the character(s) are present in your grass, and the statement does not lead directly to a species name, notice the number at the extreme right of the statement. Go to this number at the left of the page and read the adjoining statement(s). Follow this procedure until you read a statement that is followed by a botanical name. This is the name of the grass you have been trying to identify.

In using the key you may need to refer to the glossary, which immediately precedes this section. Note also that for the purpose of this key and in the descriptions of species the word blades implies and refers only to mature blades near the collar. To distinguish some characters you may need to use a ten-power hand lens. Individual characters may show some variation. Such variability, as well as changes brought about by shrinkage or distortion in dried or old material, should be taken into account when you use the key.

Vegetative-character key
1Auricles present 2
Auricles absent or rudimentary14
2Plants with rhizomes3
Plants without rhizomes7
3Rhizomes long, white; blades stiff, glaucous; collar and auricles usually purplishAgropyron smithii
Rhizomes long, yellowish white; blades not stiff, with lines of stomata on lower surfaceAgropyron repens
Rhizomes and blades not as above4
4Blades less than 10 mm wide5
Blades more than 10 mm wide6
5Rhizomes numerous; blades to 6 mm wide, flat or involute, stiff, dull greenAgropyron dasystachyum
Rhizomes few; blades to 8 mm wide, flat, lax, glossy green beneath; ligule entireFestuca elatior
Rhizomes few; blades to 10 mm wide, pale green; ligule serrateAgropyron intermedium
6Rhizomes short; often absent in old plants; ligule truncate; collar broad, continuousElymus canadensis
Rhizomes slender and scaly; ligule truncate;
collar narrow, indistinct, divided
Elymus innovatus
Rhizomes short, thick; ligule obtuse, lacerate; collar narrowElymus cinereus
7Blades more than 10 mm wide8
Blades less than 10 mm wide9
8Sheath with hyaline margins; collar broad; ligule very short, about 0.5 mm; blades green Elymus virginicus
Sheath with scarious margins; collar broad; ligule to 2 mm; blades greenElymus canadensis
Sheath with scarious margins; collar narrow; ligule to 2 mm; blades glaucousElymus glaucus
9Plants annual; blades acuminate, twisted, bluish greenLolium persicum
Plants perennial; blades not twisted10
10Blades soft pubescent on upper surfaceAgropyron cristatum
Blades not pubescent11
11Sheath usually compressed, reddish at base; blades acuminate, glossy beneathLolium perenne
Sheath not compressed, margins hyaline12
Sheath not compressed. margins scarious13
12Collar broad, continuous; blades prominently veined; no lines of stomata on lower surface; ligule truncateElymus junceus
Collar broad, continuous, constricted at midrib; blades strongly veined, firm, rigid, with lines of stomata on lower surface; ligule acuteElymus angustus
Collar distinct, continuous; blades firm, midrib prominent near collar; ligule serrate, very shortAgropyron elongatum
Collar indistinct; blades not prominently veined; ligule truncateAgrohordeum macounii
13Plants densely tufted; collar continuous; midrib prominent on lower surface of blade; sheath glabrousAgropyron spicatum
Plants loosely tufted; collar divided; midrib not prominent on lower surface of blade; sheath pubescentAgropyron subsecundum
14Plants with rhizomes15
Plants without rhizomes; roots fibrous45
15Tips of blades boat-shaped16
Tips of blades acute or acuminate19
16Ligule to 5 mm long, white, acuminate; sheath with crossveins17
Ligule to 3 mm long, greenish, truncate to acute; sheath without crossveins18
17Blades narrow, to 6 mm wide; sheath tinged with purple; blades not conspicuously crossveinedGlyceria striata
Blades broad, to 15 mm wide; sheath pale green; blades conspicuously crossveinedGlyceria grandis
18Sheath strongly flattened, sharply keeled; collar divided; blades bluish greenPoa compressa
Sheath not strongly flattened or keeled; collar continuous; blades glossy dark greenPoa pratensis
Sheath not strongly flattened or keeled; collar usually continuous; blades bluish greenPoa glaucifolia
19Blades more than 10 mm wide20
Blades less than 10 mm wide25
20Sheath closed to near the top21
Sheath split22
21Midrib of blade extending part way down sheath; blade and sheath often pubescent; sheath purplish at baseBromus pumpellianus
Midrib of blade not extending down sheath; blade and sheath glabrous; sheath not purplish at baseBromus inermis
22Plants of dry habitats23
Plants of wet habitats24
23Sheath margins hyaline; sheath usually somewhat pubescent above, light greenCalamovilfa longifolia
Sheath margins scabrous and villose; sheath glabrous, strongly veinedPanicum virgatum
24Ligule membranous, to 5 mm long, white, acute or obtuse; blades to 15 mm widePhalaris arundinacea
Ligule a fringe of hairs; blades to 15 mm wide, distinctly veined, smooth and shiny belowSpartina pectinata
Ligule a fringe of hairs; blades to 30 mm wide, not distinctly veined, dull belowPhragmites communis
25Rhizomes very short or absent26
Rhizomes elongated33
26Emerging leaves folded27
Emerging leaves rolled28
27Blade strongly veined; ligule very short; collar indistinct; plants loosely tuftedFestuca rubra
Blade strongly veined; ligule very short; collar indistinct; plants densely tuftedFestuca hallii
Blade not strongly veined; ligule to 2 mm long; collar broad, continuousAndropogon scoparius
28Ligule a fringe of hairs29
Ligule membranous30
29Blades to 7 mm wide, twisted; sheath usually pubescentBouteloua curtipendula
Blades to 3 mm wide, usually strongly curled; sheath glabrous or somewhat piloseBouteloua gracilis
30Sheath compressed or flattened, pubescent or scabrous31
Sheath round, glabrous32
31Plants densely tufted, blades to 3 mm wide; ligule very short, ciliateSporobolus heterolepis
Plants not densely tufted; blades to 10 mm wide; ligule to 3 mm long, ciliate or lacerateAndropogon gerardii
32Blades basal, glossy green, usually convolute Oryzopsis asperifolia
Blades erect or drooping, dull green, flatAgropyron trachycaulum
33Emerging leaves folded34
Emerging leaves rolled37
34Plants aquatic; blades soft and flatCatabrosa aquatica
Plants not aquatic; blades not soft35
35Ligule a fringe of hairs; sheath with scarious margins; plants sod-formingDistichlis stricta
Ligule membranous; sheath with hyaline margins; plants tufted36
36Blades to 6 mm wide; rather lax, to 15 cm long; plants loosely tuftedMuhlenbergia racemosa
Blades to 2 mm wide, rather stiff, rarely more than 5 an long; plants loosely tuftedMuhlenbergia asperifolia
Blades to 2 mm wide; rather stiff, to 10 cm long; plants densely tuftedMuhlenbergia richardsonis
37Ligule a fringe of hairsSpartina gracilis
Ligule membranous38
38Sheath dosed in early stages, splitting in middle at maturity, purplish at baseSchizachne purpurascens
Sheath split39
39Sheath with scarious margins40
Sheath with hyaline margins42
40Plants with distinctive odor when crushed Hierochloe odorata
Plants without odor when crushed41
41Blades rather lax, to 10 mm wide; collar glabrousCalamagrostis canadensis
Blades lax, to 4 mm wide; collar pubescentCalamagrostis rubescens
Blades stiff, to 4 mm wide; collar glabrousCalamagrostis inexpansa
42Blades narrow, usually less than 5 mm wide43
Blades usually more than 5 mm wide44
43Plants of dry prairie; ligule acute, to 7 mm long; blades bluish greenCalamagrostis montanensis
Plants of marshland; ligule truncate, to 4 mm long; blades greenCalamagrostis neglecta
44Plants tufted; blades short, usually less than 15 cm long; woodlands and moist prairiePhleum alpinum
Plants not tufted; blades to 50 cm long; moist prairieSorghastrum nutans
Plants not tufted; blades to 35 cm long; wetland and slough marginsScolochloa festucacea
45Ligule a fringe of hairs or absent46
Ligule membranous54
46Blades 10 mm or more wide; annuals47
Blades less than 10 mm wide49
47Ligule absent; sheath compressed, keeled; shoots prostrate or ascendingEchinochloa crusgalii
Ligule present; sheath compressed or round; shoots erect48
48Sheath compressed, keeled, glabrous; blades pubescent at baseSetaria glauca
Sheath compressed, not keeled, pubescent; blades not pubescent at baseSetaria viridis
Sheath round, conspicuously pubescent; blades pubescent on both surfacesPanicum capillare
49Plants annual, prostrate, mat-forming; blade to 3 cm long, stiffMunroa squarrosa
Plants perennial, not prostrate; blade longer than 3 cm50
50Emerging leaves folded51
Emerging leaves rolled53
51Sheath margins hyaline; sheath long-pubescent; blades long-pubescent on lower surface, sparsely pubescent aboveDanthonia intermedia
Sheath margins scarious; sheath and blades not as above52
52Plants pilose-pubescent; collar distinct, broad; blade narrow, to 15 cm longDanthonia unispicata
Plants sparsely pubescent; collar indistinct, narrow; blade narrow, to 15 cm long, curledDanthonia spicata
Plants almost glabrous; collar narrow; blades to 25 cm longDanthonia parryi
53Plants usually decumbent, spreading; blades distinctly veined, tapering to a pointSporobolus cryptandrus
Plants elect; blades not distinctly veined, bristle-like and often curledAristida longiseta
54Tips of blades boat-shaped55
Tips of blades not boat-shaped60
55Plants annual, low; shoots usually decumbent; blades short, often cross-wrinkledPoa annua
Plants perennial, mostly erect56
56Plants short-stoloniferous; blades glossy light greenPoa trivialis
Plants not stoloniferous57
57Plants densely tufted58
Plants loosely tufted59
58Shoots very flat, broad; blades flat to folded, erect, to 5 mm wide, light green; ligule to 5 mm longHelictotrichon hookeri
Shoots not very flat, small; blades folded, often bristle-like, to 3 mm wide, dark bluish green; ligule to 1 mm longPoa cusickii
Shoots not very flat, small; blades flat to folded, to 2 mm wide, green; ligule to 3 mm longPoa sandbergii
59Plants tall, decumbent at base; blades lax, broad at basePoa palustris
Plants not tall, not decumbent at base; blades stiff, linearPoa canbyi
60Emerging leaves folded61
Emerging leaves rolled70
61Ligule conspicuous, to 10 mm long62
Ligule inconspicuous, to 1 mm long63
62Blades to 10 mm wide, flat, long, indistinctly veinedDactylis glomerata
Blades to 5 mm wide, flat, long, prominently veined, translucent between veinsDeschampsia caespitosa
Blades to 2 mm wide, short, flexuous, indistinctly veinedSchedonnardus paniculatus
63Blades flat to folded or involute64
Blades filiform68
64Plants with hard, bulb-like bases; blades tapering to a fine point, dull green; collar glabrousMuhlenbergia cuspidata
Plants without bulb-like bases65
65Ligule very short, less than 1 mm long66
Ligule at least 1 mm long67
66Blades short, mostly less than 12 cm long, to 4 mm wide, blue greenKoeleria gracilis
Blades to 50 cm long, to 4 mm wide, gray greenFestuca campestris
67Ligule about 1 mm long, hyaline to whitish, blunt to roundedOryzopsis canadensis
Ligule 1 to 3 mm long, white, usually notched, pubescentOryzopsis pungens
68Plants annual, not densely tuftedFestuca octoflora
Plants perennial, densely tufted69
69Plants bluish or gray green; veins indistinct; blades to 25 cm longFestuca idahoensis
Plants bluish or gray green; veins distinct; blades to 15 cm longFestuca ovina
Plants gray green; veins distinct; blades to 50 cm longFestuca campestris
70Ligule conspicuous, usually more than 3 mm long71
Ligule inconspicuous, less than 3 mm long78
71Plants ascending from spreading base; stoloniferousAgrostis stolonifera
Plants not stoloniferous72
72Sheath margins scarious73
Sheath margins hyaline74
73Plants often densely tufted, erect, bluish green; blades indistinctly veined saline and alkaline habitatsPuccinellia nuttalliana
Plants not densely tufted, often decumbent, dull green; blades distinctly veined; wet habitatsAlopecurus aequalis
74Plants annual; blades to 12 mm wide, twisted near tip; dry habitatsPhalaris canariensis
Plants annual; blades to 12 mm wide, not twisted near tip; wet habitatsBeckmannia syzigachne
Plants perennial75
75Blades to 12 mm wide, lax; sheath prominently veined, purplish at baseCinna latifolia
Blades to 5 mm wide76
76Plants of moist habitats; blades indistinctly veined, flat, thinSphenopholis obtusata
Plants o dry habitats; blades distinctly veined, flat or involute, firm77
77Blades usually strongly involute, very long; ligule very conspicuous, to 8 mm longOryzopsis hymenoides
Blades flat to involute or convolute; ligule conspicuous, obtuse or truncate, to 4 mm longStipa comata
Blades flat to involute or convolute; ligule conspicuous, obtuse or truncate, irregular, to 5 mm longStipa spartea
78Plants annual, pubescent; sheath closed to near top79
Plants perennial, or if annual, not pubescent80
79Plants short; blades to 12 cm long, sharp-pointed; collar distinct; sheath pubescentBromus tectorum
Plants tall; blades to 30 cm long, tapering, collar indistinct; sheath retrorsely piloseBromus marginatus
80Sheath closed to near top; blades to 10 mm wide, pubescentBromus ciliatus
Sheath split, with scarious margins81
Sheath split, with hyaline margins83
81Collar and sheath long-pubescent at marginsStipa viridula
Collar not pubescent82
82Blades to 15 mm wide, bluish green, flat and lax; sheath glabrousElymus glaucus
Blades to 10 mm wide, dark green, flat or involute; lower sheath pubescentAgropyron subsecundum
Blades to 5 mm wide, light green, flat to convolute; sheath glabrousAgropyron spicatum
83Blades 10 mm wide or more84
Blades less than 10 mm wide85
84Basal leaves prostrate; collar very narrow, often indistinct, glabrous; blades flatOryzopsis asperifolia
Basal leaves erect; collar broad; margins ciliate; base of shoots bulbous; blades twistedPhleum pratense
Basal leaves erect; collar broad, glabrous; blades not twistedElymus virginicus
85Plants annual; sheath prominently veined, keeled; blades twistedLolium persicum
Plants perennial86
86Blades soft pubescent, grayish green; collar fairly broad, continuous, pale greenHordeum jubatum
Blades not pubescent, or only slightly so87
87Plants stoloniferous88
Plants not stoloniferous89
88Ligule short, truncate; blades unevenly veined, veins faint at baseAlopecurus pratensis
Ligule long, acute; blades evenly veined, veins equally evident at baseAgrostis stolonifera var. major
89Blades to 15 cm long; Iigule more than I mm long90
Blades more than 15 cm long; ligule to 1 mm long91
90Plants glabrous; blades short, usually less than 2 mm wide, sharp-pointedAgrostis scabra
Plants somewhat pubescent, especially at collar; blades to 5 mm wide, buntTrisetum spicatum
91Sheath somewhat flattened, glabrous; blades linear, bristle-like when dry, glabrousStipa richardsonii
Sheath round, lower sheath pubescent; blades flat to involute, scabrousAgrohordeum macounii
Sheath round, glabrous or softly puberulent; blades flat to involute, finely pubescentSitanion hystrix

Other Documents in the Series

  Prairie Grasses: Identified and Described by Vegetative Characteristics
Prairie Grasses: The Grass Plant
Prairie Grasses: How to Identify a Grass - Current Document
Prairie Grasses: Index of Latin Names
Prairie Grasses: Index of Common Names
  For more information about the content of this document, contact Grant Lastiwka.
This document is maintained by Linda Hunt.
This information published to the web on March 19, 2004.
Last Reviewed/Revised on March 5, 2015.

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