Common Grasses Technical Key

Common Grass Genera

To use this identification key you will need a good hand lens or magnifying glass and the plants must be in flower/fruiting stage. The key is arranged in such a way that you always have two choices, a or b, with subsequent choices dependent upon the prior choice. Successful navigation requires that you consider both a and b for each number before making the choice. If neither a nor b seems appropriate, backup to the previous number and re-examine the choices. The number of species in the state for that genus is listed in parentheses. Refer to the introduction ("The grass plant") for help with structural terms. Feedback is appreciated; please send a separate email message to

1) a. Spikelets all unisexual (carpellate spikelets in upper part of
inflorescence, staminate in lower)
b. Spikelets with at least 1 perfect floret (anthers may be lost after maturity but spikelets look similar throughout inflorescence) # 2
2) a. Plants at least 1.5 m tall at maturity Phragmites
b. Plants under 1.5 m tall #3
3) a. Spikelets covered with spines Cenchrus
b. Spikelets not spiny #4
4) a. Glumes absent Leersia
b. At least 1 glume present, though sometimes minute #5
5) a. Spikelets with only 1 fertile floret #6
b. Spikelets with 2 or more fertile florets #28
6) a. Spikelets with 1 or more sterile florets present (spikelets therefore with at least 2 florets) #7
b. Spikelets with just 1 floret #16
7) a. Spikelets paired at each node, usually one is sessile/subsessile and one pediceled; the pediceled spikelet staminate, neuter, or represented by a pedicel only #8
b. Spikelets not paired or if paired not as in 7)a. #10
8) a. Spikelets arranged in a panicle; pedicellate spikelet represented by pedicel only Sorghastrum
b. Spikelets arranged in a raceme; pedicellate spikelet present #9
9) a. Branches of inflorescence terminating in a single spike-like raceme Schizachyrium
b. Branches of inflorescence terminating in a cluster of spike-like racemes Andropogon
10) a. Sterile florets present above the fertile floret Bouteloua
b. Sterile florets present below the fertile floret #11
11) a. Sterile floret 1; second glume similar to sterile lemma #12
b. Sterile florets 2; second glume not similar to sterile lemma #15
12) a. Spikelets subtended by long bristles Setaria
b. Bristles lacking #13
13) a. Fertile lemma hardened at maturity, margins generally inrolled over palea #14
b. Fertile lemma thin, margins not inrolled over palea Digitaria
14) a. Spikelet awned; second glume and sterile lemma with stiff hairs over the back; tip of fertile palea enclosed by the fertile lemma Echinochloa
b. Spikelets awnless and hairless; tip of fertile palea generally visible Panicum
15) a. Sterile florets staminate Hierochloe
b. Sterile florets represented by hairy scales Phalaris
16) a. Awns lacking #17
b. Awns present on either glumes or lemmas (look carefully as these may break off in old material) #20
17) a. Glumes as long as or longer than the lemma #18
b. At least the first glume shorter than the lemma #19
18) a. Callus long-hairy; palea present Calamagrostis
b. Callus not long-hairy; palea absent or poorly developed Agrostis
19) a. Lemma 3-nerved Muhlenbergia
b. Lemma 1-nerved Sporobolus
20) a. Spikelets all turned to one side and crowded Spartina
b. Spikelets not as above #21
21) a. Disarticulation below the spikelet (so that after fruits have shed only the main stalk of the inflorescence remains) Alopecurus
b. Disarticulation above the glumes (at least some glumes remain on the inflorescence after fruit have dropped) #22
22) a. Lemma hardened, awned #23
b. Lemma not hardened, awned or awnless #25
23) a. Awn 3-branched Aristida
b. Awn unbranched #24
24) a. Awn straight or curved but not twisted or coiled Oryzopsis
b. Awn twisted or coiled several times at least near base Stipa
25) a. Glumes equal in size and shape, apex broad and abruptly short-awned Phleum
b. Glumes unequal or apex narrow or tapering #26
26) a. Lemma awned from the back or from near base; glumes equaling or longer than the lemma #27
b. Lemma awned from apex; at least the 1st glume shorter than the lemma Muhlenbergia
27) a. Callus long-hairy; palea present, appearing as a translucent stiffer hair; rachilla present Calamagrostis
b. Callus not long-hairy; palea absent or poorly developed; rachilla absent Agrostis
28) a. Inflorescence a spike (1 or more spikelets per node) #29
b. Inflorescence a panicle #32
29) a. Spikelets all solitary at nodes of the inflorescence #30
b. Spikelets 2 or more per node #31
30) a. Plants bunchgrasses Elymus (E. trachycaulus)
b. Plants rhizomatous Elytrigia
31) a. Spikelets 3 at each node; the laterals reduced and pedicellate Hordeum
b. Spikelets 2-4 per node; all fertile Elymus
32) a. Lemmas awned #33
b. Lemmas awnless #36
33) a. First glume 3 or 5-nerved #34
b. First glume 1 or 3-nerved #35
34) a. Callus long hairy; leaf sheaths open Schizachne
b. Callus not hairy; leaf sheaths closed Bromus
35) a. Lemma apex bifid (sometimes the apex is minutely bifid with the awn appearing to be attached just below the apex); spikelets over 1.5 cm long Bromus
b. Lemma apex acute or minutely bifid; spikelets under 1.2 cm long Festuca
36) a. Nerves of lemma parallel #37
b. Nerves of lemma curving towards apex, not parallel #38
37) a. Lemmas 3-nerved; plants under 3 dm tall Eragrostis
b. Lemmas 5-nerved; plants over 3 dam tall Glyceria
38) a. Lemmas 5-nerved #39
b. Lemmas 7-nerved Bromus
39) a. Lemma apex acute to acuminate, rounded on the back #40
b. Lemma apex obtuse to acute, keeled on the back Poa
40) a. Glumes as long as the lemmas; spikelets mostly 2-flowered Koeleria
b. Glumes clearly shorter than the lemmas; spikelets several flowered Festuca

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Copyright 2002, A.F. Cholewa, J.F. Bell Museum of Natural History, University of Minnesota / No portion of this guide may be duplicated without written permission of author.