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Key to Poaceae

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1 Plant a shrub or tree (the culms perennial, woody, to 25 m tall), with complex branching systems from the upper nodes; leaves strongly dimorphic, those of the main culm sheathing, those of the branches or culm tips pseudopetiolate
1 Plant an herb (the culms annual, not truly woody, to 5 m tall), lacking complex branching systems from the upper nodes; leaves not dimorphic, none of them pseudopetiolate.
  2 Plant a robust grass, culms usually > 2 m tall and usually > 5 mm in diameter at the base
  2 Plant a small to medium grass, culms < 2 m tall and usually also < 5 mm in diameter at the base.
    3 Spikelets either modified into asexual, purplish bulblets, or partially or wholly concealed either by spines, hooks, and/or involucres, or partially or wholly concealed by being imbedded in a fleshy rachis or cob.
      4 Fertile spikelets either absent (spikelets modified into asexual, purplish bulblets) or variously spiny or bead like
      4 Fertile spikelets embedded in a fleshy rachis (resembling a rattail) or a cob
    3 Spikelets apparent, not covered, concealed, embedded, or modified by spines, hooks, or involucres.
        5 Spikelets 2-flowered, often dorsally compressed, falling entire at maturity (the abscission below the glumes), the upper floret usually bisexual, the lower one male or sterile.
          6 Glumes often as long as or longer than the lemmas and concealing the florets; spikelets usually arranged in obvious pairs or triplets, with 1 spikelet sessile or shortly pedicellate and the other 1 (or 2) spikelets pedicellate (the pedicellate sometimes vestigial or absent)
          6 Glumes (the lower or both) shorter than the lemmas (or the glumes absent); spikelets not organized in pairs or triplets
        5 Spikelets 1-, 2-, or many-flowered, usually terete or somewhat laterally compressed, either abscising at maturity above the glumes or if 2-flowered then both florets bisexual, or the upper sterile.
             7 Inflorescence of one or more spikes, the spikelets sessile (or very short-pedicelled) on the spike axis, 1-more per node, characteristically in 2-more ranks (these either on opposite sides of the axis or crowded on one side), the individual spikelets borne more-or-less touching one another.
               8 Spikelets borne in a single terminal spike or raceme (an extension of the culm), usually 2-ranked on opposite sides of the axis
               8 Spikelets borne on 1-many spikes (the spikes themselves arranged digitately, subdigitately, or racemosely on the culm) in 2 (or more) rows; spikelets often on one side of the spike axis
             7 Inflorescence paniculate, sometimes somewhat to very congested, but then not as above.
                 9 Spikelets with a single bisexual floret, and no staminate, sterile, or reduced florets present (occasional spikelets of Muhlenbergia can have 2-3 florets).
                   10 Glumes present; palea various; [habitats various].
                     11 Inflorescences dense and spikelike, symmetrical, cylindrical or ovoid, unbranched
                     11 Inflorescences loose and open, or if relatively dense, then with discernible branches, and thus lobed or asymmetrical.
                 9 Spikelets with 2-many florets, including bisexual, staminate, reduced, or sterile flowers.
                          13 Glumes (one or both) nearly equaling or surpassing the most apical lemma of the spikelet, therefore partially or completely concealing the florets

Key to Poaceae, Key A: bamboo grasses (woody trees and shrub grasses) (tribe Bambuseae)

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1 Rhizomes pachymorph, having root-bearing internodes thicker than the culm; culms usually in single clumps
1 Rhizomes leptomorph, root-bearing internodes thinner than the culm; culms solitary or in many connected clumps.
  2 Mid-culm branches consistently 2, unequal, rarely with a smaller central third branch
  2 Mid-culm branches not consistently 2, initially 1-9.
    3 Dwarf bamboos, < 1 (-1.5) m tall.
      4 Leaf blade margins not or only slightly bleached in winter, terminal blade parallel to shoot axis, blades often variegated
      4 Leaf blade margins more or less bleached in winter, terminal blade often angled from shoot axis, blades usually not variegated
    3 Medium-stature to tall bamboos, > 1 m tall.
        5 Mid-culm branches initially 5-9
        5 Mid-culm branches initially 1-3 (-5).
          6 Mid-culm branches (1-) 2-7; branches and leaves small to medium relative to culm size; [native]
          6 Mid-culm branches 1 (-3); branch and leaves often very large relative to culm size; [exotic].
             7 Leaf blade margins not bleached in winter, terminal blade parallel to shoot axis; culm buds initially open or closed
             7 Leaf blade margins bleached in winter, terminal blade often deflexed from shoot axis; culm buds initially closed

Key to Poaceae, Key B: robust herbaceous grasses

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1 Inflorescence an array of spikes, the spikelets closely imbricate in 2 rows along the rachis of the spikes, the spikes alternate along the primary inflorescence axis; [tribe Zoysieae; subtribe Sporobolinae]
1 Inflorescence otherwise, either the spikelets embedded or in grooves in an thickened rachis, or the inflorescence a slender or broad panicle.
  2 Spikelets embedded in the thickened rachis (the inflorescence thus like an ear of corn), or fitting into grooves in the thickened rachis (the inflorescence thus cylindrical and resembling a rat's tail). Spikelets unisexual, with male and female spikelets in separate inflorescences or in different parts of the same inflorescence; [tribe Andropogoneae].
    3 Racemes of mixed sex (female below, male above)
    3 Racemes of single sex
 Zea
  2 Spikelets not embedded or fitting into grooves in the rachis, the inflorescence a slender or broad panicle (the spikelets visibly separate and often pedicelled).
      4 Spikelets with a single floret, this unisexual (either pistillate or staminate); plants with aerenchymatous culms, [plants of seasonally or tidally flooded wetlands]; [tribe Oryzeae].
        5 Pistillate spikelets on the upper branches of the panicle, staminate spikelets on the lower branches; lemmas and paleas clasping along their margins; plants annual
        5 Pistillate and staminate spikelets intermingled on the same branches of the inflorescence; lemma margins free; plants perennial
      4 Spikelets with 2 or more florets, at least some of these bisexual; plants without aerenchymatous culms, [plants of uplands or temporarily to seasonally flooded wetlands].
          6 Spikelets with 2-8 florets, these bisexual.
             7 Leaves primarily basal, plants densely cespitose.
               8 Panicles plumose; [tribe Danthonieae]
             7 Leaves cauline; plants short-rhizomatous (somewhat clumped) to long-rhizomatous; [tribe Arundineae].
                 9 Lemmas pilose; rachilla glabrous; plants short-rhizomatous (somewhat clumped); culms to 10 m tall; [plants of uplands or saturated or temporarily flooded wetlands]
                 9 Lemmas glabrous; rachilla sericeous; plants long rhizomatous; culms to 4 m tall; [plants of uplands or saturated, tidally flooded, or seasonally flooded wetlands]
          6 Spikelets almost always with 2 florets, the lower florets sterile or staminate (sometimes reduced to lemmas or completely absent).
                   10 Spikelets falling separately, not attached to rachis segments, stalks, or bristles; spikelets <2× as long as wide; [tribe Paniceae].
                     11 Spikelets (at least the terminal) subtended by 1-many stiff, terete bristles
                     11 Spikelets not subtended by stiff bristles.
                   10 Spikelets falling with attached rachis segments, stalks, or bristles; spikelets >3× as long as wide; [tribe Andropogoneae].
                          13 Pedicelled spikelet differing from the sessile in shape and sex (sometimes represented only by a pedicel).
                              15 Pedicelled spikelet represented by pedicel only; apex of sheath bearing 2 auricles 1-10 mm long; [native]
                                16 Spikelets falling in pairs together with sections of the disarticulating rachis
                                  17 Spikelets awned with awns 10-26 mm long; anthers 2; [native, collectively common and widespread]
                                  17 Spikelets unawned or with awns to 5.2 mm long; anthers 3; [exotic, rarely encountered]

Key to Poaceae, Key C: bur, bead, or bulblet grasses of various tribes

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1 Fertile spikelets absent (spikelets modified into asexual, purplish bulblets) or variously spiny or bead like; [tribe Poeae]
 Poa
1 Fertile spikelets variously spiny or bead-like.
  2 Pistillate spikelets concealed within a hard, beadlike shell, this white, black, or variously colored; [tribe Andropogoneae]
  2 Spikelets concealed in a variously spiny bur, this green or tan, sometimes with pink or purple shading.
    3 Bur formed from accrescent branchlets, with fewer and less regularly arranged straight prickles (these typically retrorsely scabrous); [tribe Paniceae]
    3 Bur formed from an enlarged glume, with 5-7 rows of hooked prickles; [tribe Cynodonteae; subtribe Traginae]

Key to Poaceae, Key D: rattail or cob grasses

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1 All spikelets unisexual, the pistillate and staminate spikelets either in separate inflorescences, or the pistillate spikelets below the staminate spikelets in the same inflorescence; leaves 9-120 mm wide; [tribe Andropogoneae].
  2 Pistillate spikelets below the staminate in the same inflorescence
  2 Pistillate and staminate spikelets in separate inflorescences, the pistillate inflorescences axillary, staminate inflorescences terminal
 Zea
1 Some spikelets bisexual; leaves 1-25 mm wide.
    3 Spikelets with 2-7 florets, the lower bisexual and fertile, the upper sometimes sterile; [tribe Triticeae]
    3 Spikelets with at most 2 florets, the lower staminate or sterile, the upper bisexual, staminate, or sterile.
      4 Culms 2-45 cm tall; leaves 1-6 mm wide; plants annual (perennial in Eremochloa and Stenotaphrum).
        5 Plants obviously and prominently rhizomatous (Eremochloa) or stoloniferous (Stenotaphrum); lower glume with pectinate margins (Eremochloa) or irregularly toothed (Stenotaphrum)
          6 Plant rhizomatous; lower glume with pectinate margins; [commonly naturalized turf grass and roadside weed]; [tribe Andropogoneae]
          6 Plant stoloniferous; lower glume irregularly toothed; [naturalized turf grass and allegedly also native]; [tribe Paniceae]
        5 Plants annual; lower glume with smooth and cartilaginous margins (or absent); [rare waifs]; [tribe Poeae].
             7 Spikelets with 2 glumes
      4 Culms 30-400 cm tall; leaves 2-25 mm wide; plants annual or perennial; [tribe Andropogoneae].
               8 Lower glumes of the sessile spikelets rough, rugose, pitted, tuberculate or alveolate between the keels
               8 Lower glumes of the sessile spikelets smooth or scabrous.
                 9 Pedicels at least partially fused to the rame axes
                   10 Sheaths mostly glabrous (sparsely ciliate towards the base); plants perennial
                   10 Sheaths with stiff, papillose-based hairs 1-3 mm long; plants annual
                 9 Pedicels appressed, but not fused, to the rame axes.

Key to Poaceae, Key E: grasses of tribe Andropogoneae (also including grasses also keyed in Keys B, C, and D)

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1 Leaves ovate-lanceolate, 2-10 cm long, 2.5-7× as long as wide; plants weak-stemmed annuals, branching, decumbent, rooting at the lower nodes; [exotic weeds].
  2 Leaves cordate-clasping at base; spikelets not paired, unaccompanied by a vestige
  2 Leaves tapering to a broadly cuneate base; spikelets paired (one of the pair sometimes vestigial)
1 Leaves lanceolate to linear, either longer or proportionately narrower; plants either perennial or coarse annuals with erect and mostly unbranched culms.
    3 Spikelets embedded in the thickened rachis (the inflorescence thus like an ear of corn), or fitting into grooves in the thickened rachis (the inflorescence thus cylindrical and resembling a rat's tail), or the pistillate inflorescences enclosed in a hard, bead-like, pearly-white, modified bract.
      4 Spikelets unisexual, with male and female spikelets in separate inflorescences or in different parts of the same inflorescence.
        5 Internode narrower than and more-or-less enclosed by the female spikelet
        5 Internode broader than and more-or-less enclosing the female spikelet.
          6 Racemes of mixed sex, female flowers below, and male above
          6 Racemes of single sex, the female inflorescences (“ears”) borne on axillary branches, the male inflorescences (“tassels”) terminal on the culm
 Zea
      4 Spikelets, or at least one of each pair, bisexual.
             7 Culms 2-45 cm tall; leaves 1-5 mm wide; plants perennial, obviously and prominently rhizomatous; lower glume with pectinate margins; [commonly naturalized turf grass and roadside weed]
             7 Culms 30-400 cm tall; leaves 2-25 mm wide; plants annual or perennial, cespitose or short-rhizomatous; lower glume winged or not, but not pectinate.
               8 Lower glumes of the sessile spikelets rough, rugose, pitted, tuberculate or alveolate between the keels
               8 Lower glumes of the sessile spikelets smooth or scabrous.
                 9 Pedicels at least partially fused to the rame axes
                 9 Pedicels appressed, but not fused, to the rame axes
    3 Spikelets not embedded or fitting into grooves in the rachis, the rachis slender (the spikelets visibly separate and often pedicelled).
                     11 Pedicelled spikelet similar to the sessile spikelet, both fertile.
                       12 Spikelets falling separately from the persistent rachis.
                       12 Spikelets falling in pairs together with sections of the disarticulating rachis.
                            14 Spikelets awned with awns 10-26 mm long; anthers 2; [native, collectively common and widespread]
                            14 Spikelets unawned or with awns to 5.2 mm long; anthers 3; [exotic, rarely encountered]
                     11 Pedicelled spikelet differing from the sessile in shape and sex (sometimes represented only by a pedicel).
                                16 Spikelets with or without awns, if awned the awns < 5 cm long.
                                       19 Pedicelled spikelet represented by pedicel only; apex of sheath bearing 2 auricles 1-10 mm long; [native]
                                           21 Pedicels of the pedicelled (reduced or absent) spikelets terete or slightly flattened and grooved on one side only
                                           21 Pedicels of the pedicelled (reduced or absent) spikelets strongly flattened and with or without grooves on both sides.
                                             22 Rame internodes and pedicels with a translucent medial groove; pedicelled spikelets smaller than the sessile spikelets (or vestigial/absent)
                                             22 Rame internodes and pedicels without a translucent medial groove; pedicelled spikelets ca. the same size as sessile spikelets

Key to Poaceae, Key F: grasses of tribe Paniceae (also including grasses keyed as well in Keys B, C, D, and H)

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1 Inflorescences spikelike branches, the spikelets partially embedded in the rachises
1 Inflorescences panicles or spikes (if spikes, the spikelets not embedded.
  2 Spikelets (at least the terminal) subtended by 1-many stiff, terete bristles.
    3 Bristles persistent on the inflorescence, each spikelet disarticulating above the bristles
    3 Bristles falling with the spikelets at maturity (the disarticulation at the base of the fascicles)
  2 Spikelets not subtended by stiff bristles.
      4 Inflorescences of spikelike branches 1-3.7 cm long, the branch extending 2.5-4 mm beyond the attachment of the distal spikelets
      4 Inflorescences not as above.
        5 Upper florets laterally compressed
        5 Upper florets dorsally compressed.
          6 Lower glumes or lower lemmas awned.
             7 Leaves > 10× as long as wide; ligules absent or of hairs
             7 Leaves < 8× as long as wide; ligules present, membranous or of hairs.
               8 Lower glumes unawned or very shortly so; upper glumes ciliate-margined; plants erect or basally decumbent
               8 Lower glumes awned; upper glumes not ciliate-margined; culms trailing; plants strongly trailing, rooting at the nodes
          6 Lower glumes and lower lemmas unawned.
                 9 Lemma margins flat, hyaline; lower glumes absent or < ¼ the length of the upper glume.
                   10 Subterranean (cleistogamous) inflorescences present; aerial inflorescences with elongate rachises; spikelets of the aerial inflorescences often sterile; spikelets glabrous; leaves either with a white cartilaginous margin or prominently ciliate; [of the Coastal Plain]
                   10 Subterranean inflorescences absent; aerial inflorescences either with digitate or subdigitate branches and glabrous spikelets, or with elongate rachises and conspicuously pubescent spikelets; spikelets of the aerial inflorescences fertile; spikelets glabrous, ciliate, or pubescent; leaves various (often not as above); [collectively widespread]
                     11 Inflorescence a narrow panicle with the branches strongly ascending to appressed; spikelets ellipsoid to obovoid; [of Coastal Plain pinelands]
                     11 Inflorescence either a panicle with digitate or subdigitate clusters of spikelike branches or a broad panicle with widely divergent branches; [widespread]
                 9 Lemma margins not hyaline, frequently involute; lower glumes various (absent, < ¼ the length, to longer than the upper glume).
                       12 Spikelets not subtended by a cuplike callus.
                          13 Leaves primarily lacking ligules (at least the upper, and often all, leaves without ligules, if vestigial ligules present, these of hairs)
                          13 Leaves with ligules, these either membranous or of hairs.
                            14 Lower (sterile) palea indurate and expanding the spikelet at maturity, as long as the lower (sterile) lemma; lower and upper florets standing apart from one another at maturity; outer surface of the upper (fertile) palea with compound papillae
                            14 Lower (sterile) palea membranous, not expanding the spikelet at maturity, usually shorter than lower (sterile) lemma, or absent; lower and upper florets closely appressed at maturity; outer surface of the upper (fertile) palea lacking compound papillae.
                                16 Spikelets with lower lemmas (and lower glumes, if present) adjacent to the branch axes.
                                  17 Lower glumes present on at least most spikelets
                                16 Spikelets with upper lemmas (and upper glumes, if present) adjacent or appressed to the branch axes.
                                    18 Upper or both glumes present on all spikelets.
                                       19 Lower glumes usually absent; upper lemmas smooth to slightly rugose
                              15 Inflorescence either paniculate with well-developed secondary branchlets or if the primary branches spikelike, then the spikelets not borne in a 1-sided arrangement on the spicate branches.
                                         20 Inflorescences dense, the spikelets obscuring most of the internal branches
                                         20 Inflorescences open panicles, or if narrowed, all or nearly all the panicle branches readily visible.
                                           21 First glume 5-7.5 mm long, nearly as long as sterile lemma; fertile lemma 1/3 length of sterile lemma; rachilla prolonged between the florets
                                           21 First glume shorter, or if this long, then at most 3/4 length of sterile lemma; fertile lemma > ½ the length of the sterile lemma; rachilla not prolonged between the florets.
                                             22 Plant developing a terminal (“spring”) inflorescence usually before mid-summer, followed by lateral (“autumnal”) inflorescences from lower, mid, and/or upper nodes, these often included or hidden among the fascicles of smaller “autumnal” leaves; often developing a rosette of overwintering basal leaves
                                             22 Plant developing a terminal inflorescence usually after mid-summer, the lateral inflorescences, when present, from the upper nodes, usually appearing at the same time as the terminal panicle, and not hidden by dense fascicles of smaller leaves; plants lacking a rosette of overwintering basal leaves.
                                                    25 Spikelets > 4.5 mm long; first glume > 2.4 mm long; ligule 4-6 mm long; [of coastal dunes]
                                                    25 Spikelets < 4 mm long; first glume < 2.1 mm long; ligule < 2 mm long; [not of coastal dunes].
                                                        27 Panicles constricted, 0.3-1.6 cm wide; spikelets subsessile to short-pediceled; summit of fertile palea not enclosed by fertile lemma
                                                        27 Panicles > 1 cm wide; spikelets short to long-pedicelled; summit of fertile palea enclosed by fertile lemma
                                                            29 Lower primary panicle branches in whorls of 4-7 at the nodes, stiffly spreading, naked on the proximal ½, the axils strongly pilose; lower culm internodes appressed papillose-pubescent; first glume acuminate, ½ as long as spikelet; fertile lemma chestnut brown at maturity
                                                                       34 Culms slightly compressed below; ligules 0.5 mm long or less; spikelet pedicels appressed, the spikelets subsecund, usually some obliquely bent above the first glume; fertile lemma 1.8-2.2 mm long
                                                                       34 Culms terete; ligules 1-6 mm long; at least some spikelet pedicels spreading, spikelets not at all secund, essentially straight; fertile lemma 2-4 mm long

Key to Poaceae, Key G: wheat grasses of tribe Triticeae (and a few unrelated mimics)

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1 Spikelets 2-7 at all or most nodes; [tribe Triticeae].
  2 Spikelets 2-5 at each node (if 3, all 3 sessile).
  2 Spikelets 3 at each node (the central spikelets usually sessile, the lateral pedicellate)
1 Spikelets 1 at all or most nodes (occasionally in pairs at lowest nodes).
    3 Spikelets borne on peduncles 0.5-2 mm long; [tribe Brachypodieae]
    3 Spikelets sessile.
      4 Spikelets (not including the awns) > 3× as long as the rachis internodes, strongly divergent (at nearly 90° to the rachis); [very rare exotic]; [tribe Triticeae]
      4 Spikelets (not including the awns) < 3× as long as the rachis internodes.
        5 Glumes subulate to narrowly lanceolate or linear, narrowing from below midlength, with 1 vein throughout or at least distally (sometimes 1-3 veins at midlength in Pascopyrum); [tribe Triticeae]
          6 Awns long, 12-26 (-35) mm; glumes keeled; spikelets with 2 (-3) florets
          6 Awns short, 5 mm or less in length; glumes not keeled; spikelets with 2-12 florets
        5 Glumes broader, narrowing from beyond midlength, with 3-9 veins at midlength.
             7 Spikelets placed edgewise to the rachis; first glume lacking except in the terminal spikelet; [tribe Poeae]
             7 Spikelets placed flatwise to the rachis; first glume present; [tribe Triticeae].
               8 Plants annuals; glumes often with lateral teeth or awns; glumes rounded or keeled; [exotics, rare out of cultivation].
                 9 Glumes rounded; spikelets in some species embedded into the thickened rachis
                 9 Glumes keeled; spikelets never embedded in a thickened rachis
               8 Plants perennials; glumes without lateral teeth or awns; glumes keeled; [natives or exotics].
                   10 Glumes acute to acuminate (and often awned); [common natives and exotics]

Key to Poaceae, Key H: finger grasses

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1 Spikelets 2-flowered, often dorsally compressed, falling entire at maturity (the abscission below the glumes), the upper floret usually bisexual, the lower one male or sterile; [tribe Paniceae]
  2 Lemma margins hyaline, flat; lower glumes various (absent, < ¼ the length, or longer than the upper glume)
  2 Lemma margins not hyaline, frequently involute; lower glumes absent or < ¼ the length of the upper glume.
    3 Spikelets with lower lemmas (and lower glumes, if present) adjacent to the branch axes.
      4 Lower glumes absent
      4 Lower glumes present on at least most spikelets
    3 Spikelets with upper lemmas (and upper glumes, if present) adjacent or appressed to the branch axes.
        5 Both glumes absent from all or most spikelets
        5 Upper or both glumes present on all spikelets.
          6 Lower glumes usually absent; upper lemmas smooth to slightly rugose
          6 Lower glumes present; upper lemmas rugose and verrucose
1 Spikelets 1-, 2-, or many-flowered, usually terete or somewhat laterally compressed, either abscising at maturing above the glumes or if 2-flowered then both florets bisexual, or the upper sterile; [tribes Cynodonteae and Zoysieae]
             7 Spikes normally solitary (rarely 2), divergent at the summit of the culm; second glume with a recurved spine arising from the back; fresh plants aromatic with a citrus odor; [tribe Cynodonteae; subtribe “incertae sedis”]
             7 Spikes normally 2 or more, alternate, digitate, subdigitate, or verticillate along the main inflorescence axis; second glume lacking a recurved spine; fresh plants not aromatic with a citrus odor.
               8 Spikes arranged along the central inflorescence axis alternately, solitary at each node.
                 9 Spikelets with 1 bisexual floret, sometimes also with modified male, sterile, or rudimentary florets above the fertile floret.
                   10 Spikelets with modified male, sterile, or rudimentary florets above the fertile floret; [plants of uplands]; [tribe Cynodonteae; subtribe Boutelouinae]
                   10 Spikelets lacking any modified florets; [plants of wetlands, primarily saline and coastal]; [tribe Zoysieae; subtribe Sporobolinae]
                 9 Spikelets with 2 or more bisexual florets (sometimes also with additional reduced florets); [tribe Cynodonteae; subtribe Eleusininae].
                     11 Ligules 4-8 (-15) mm long, acute to attenuate, entire (lacerate only by tearing)
                       12 Lemmas 3-veined; ligule (0.2-) 0.5-5.5 (-7.0) mm long; apex erose or entire
               8 Spikes arranged along the central inflorescence axis in a digitate, subdigitate, or verticillate manner, all or most nodes with 2 or more spikes; [tribe Cynodonteae].
                          13 Spikelets with 1 fertile floret (there may also be 1 or more sterile florets); [tribe Cynodonteae; subtribe Eleusininae].
                              15 Lowest lemmas awned (rarely unawned); upper glumes acute to acuminate, mucronate or short-awned
                              15 Lowest lemmas unawned (or with an awn to 1.2 mm long); upper glumes truncate or bilobed, sometimes short-awned from between the lobes
                          13 Spikelets with 2 or more fertile florets.
                                16 Spikes to 7 cm long, terminating in a point (the spikes acuminate); [tribe Cynodonteae; subtribe “incertae sedis”]
                                16 Spikes to 22 cm long, terminating in a functional or rudimentary spikelet (the spikes acute to obtuse); [tribe Cynodonteae; subtribe Eleusininae].

Key to Poaceae, Key I: rice grasses, of tribe Oryzeae (also including grasses keyed as well in Key B)

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1 Lemma margins free; plants perennial.
  2 Plants either < 1 m tall or a floating aquatic with lax stems to 1.5 m long
  2 Plants 1-4 m tall, emergent, the stems stout, not lax
1 Lemmas and paleas clasping along their margins; plants annual or perennial.
    3 Spikelets either pistillate or staminate, the upper branches of the panicle with pistillate spikelets, the lower branches with staminate spikelets; grains terete
    3 Spikelets bisexual; grains laterally flattened.
      4 Glumes absent and also lacking glume-like sterile florets subtending the floret; lemmas and paleas pectinately ciliate-hispid on the margins; [native]
      4 Glumes absent or greatly reduced, glume-like sterile florets subtending the fertile floret; lemmas and paleas glabrous or pubescent, but not pectinately ciliate hispid on the margins; [introduced]

Key to Poaceae, Key J: dense spike grasses

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1 Lemma 8-11.5 (-14) mm long; [tribe Poeae]
1 Lemma 0.5-6 mm long.
  2 Glumes awned; [tribe Poeae].
    3 Glume awns prominently pilose
    3 Glume awns not hairy
      4 Glume awn 0.7-3 mm long; lemmas not awned
      4 Glume awn 3-8 mm long; lemmas awned
  2 Glumes unawned.
        5 Lemmas much shorter than the glumes; [tribe Poeae]
        5 Lemmas about equaling or longer than the glumes.
          6 Lemmas about equaling the glumes; [tribe Poeae]
          6 Lemmas longer than the glumes; [tribe Zoysieae; subtribe Sporobolinae]

Key to Poaceae, Key K: grasses with 1 floret and unawned lemmas

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image of plant
Show caption*© Aidan Campos
1 Spikelets 18-32 mm long; [tribe Poeae]
1 Spikelets 0.7-10.8 mm long.
image of plant
Show caption*© Eric Lamb, some rights reserved (CC BY), uploaded by Eric Lamb
  2 Spikelets clearly orbiculate, the glumes keeled
  2 Spikelets variously shaped, sometimes rounded but not clearly orbiculate, the glumes keeled or not.
    3 Florets rigid, shining; glumes and lemmas rounded in ×-section, not keeled; spikelets 2.5-5 mm long; [tribe Poeae]
    3 Florets soft, papery; glumes and lemmas keeled in ×-section; spikelets 0.7-10.8 mm long.
      4 Florets with a conspicuous tuft of hairs on the callus; [tribe Zoysieae; subtribe Sporobolinae]
      4 Florets not conspicuously hairy on the callus.
        5 Lemma 1-veined; ligule of hairs; grain becoming mucilaginous when wet; [tribe Zoysieae; subtribe Sporobolinae]
        5 Lemma 1-5-veined; ligule a membrane (the summit sometimes ciliolate); grain not becoming mucilaginous when wet.
          6 Lemmas faintly 5-veined; lower glume longer than the lemma; palea much shorter than the lemma (or absent); [tribe Poeae]
          6 Lemmas strongly 3-veined; lower glume shorter than (rarely equaling) the lemma; palea about equaling the lemma; [tribe Cynodonteae; subtribe Muhlenbergiinae]

Key to Poaceae, Key L: grasses with 1 floret and awned lemmas

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1 Lemma awn 3-branched (the lateral 2 sometimes very reduced compared to the central); [tribe Aristideae]
1 Lemma awned with a simple awn.
  2 Upper glumes present, 1-veined; lower glumes absent or much shorter than the upper glumes and veinless; [tribe Brachyelytreae]
  2 Both glumes present, 1-many-veined.
    3 Lemma hardened, distinctly different than the glumes in texture when mature; [tribe Stipeae].
      4 Rhizomatous perennials; primary leaves cauline (the basal leaves < 2 cm long or merely represented by sheaths), 8-16 mm wide
      4 Cespitose perennials; primary leaves basally disposed, 0.2-10 mm wide.
        5 Leaves > 4 mm wide.
          6 Florets 2.5-3.5 mm long; awns 3.4 mm long; [exotic, rarely naturalized]
          6 Florets 5-13 mm long; awns either 7-15 or 30-120 mm long; [exotics or natives].
             7 Leaves 2-8 mm wide, not twisted at the base; awns 30-120 mm long
             7 Leaves 4-10 mm wide, the base twisted so that the abaxial surface is uppermost; awns 7-15 mm long
        5 Leaves < 4 mm wide.
               8 Florets 7-25 mm long; awns 30-225 mm long.
                 9 Palea grooved, longer than the lemma; lemma margins involute, fitting into the paleal groove; [native species, collectively widespread in our area]
                 9 Palea flat, shorter than or equal to the lemma; lemma margin convolute or not overlapping; [exotic species, rare in our area]
                   10 Lemma margins not or only slightly overlapping at maturity; awns 60-190 mm long
                   10 Lemma margins strongly overlapping for their entire length at maturity; awns 40-120 mm long
               8 Florets 1.5-4.5 mm long; awns 1-35 mm long
                     11 Leaves 0.2-0.6 mm wide; florets 1.5-2.5 mm long; awns 15-35 mm long
                     11 Leaves 0.5-10 mm wide; florets 2.2-4.5 mm long; awns 1-15 mm long.
                       12 Leaves 0.5-1.8 mm wide; central vein of the lemma not prominent; [native species]
    3 Lemma neither hardened nor distinctly different than the glumes in texture when mature.
                          13 Spikelets 18-32 mm long; [tribe Poeae]
                            14 All spikelets sessile or subsessile and arrayed along inflorescence axes (racemes) divergent from the central axis (but not both overlapping one another and clearly ranked on one side of the axis, so as to be keyed under Key H).
                              15 Inflorescences with disarticulating branches; Lower glumes 0.9-4 mm long; spikelets disarticulating below the glumes, the spikelet falling as a whole; spikelets appressed to divergent from the raceme axes; sheaths not strongly overlapping; [tribe Cynodonteae; subtribe Eleusininae]
                              15 Inflorescences without disarticulating branches; lower glumes 1.5-3 mm long (Muhlenbergia paniculata) or (2-) 3.5-7 mm long (Gymnopogon); spikelets disarticulating above the glumes (which often remain on the inflorescence); spikelets strongly appressed to the raceme axes; sheaths strongly overlapping or not , if so then at least on the upper culm, therefore hiding the culm; [tribe Cynodonteae; subtribe “incertae sedis”]
                                16 Blades with thick, white margins and well-developed midrib; inflorescence branches strongly divergent; glumes unequal, usually shorter (sometimes only slightly so) than the solitary floret
                                16 Blades lacking both thick, white margins and well-developed midribs; glumes subequal, usually exceeding the 1-2(4) floret(s)
                            14 Spikelets pedicellate and arrayed in a more complex and open panicle.
                                    18 Spikelets articulated below the glumes, the spikelet falling intact, leaving a naked pedicel; [tribe Poeae]
                                    18 Spikelets articulated above the glumes, the floret falling, leaving the glumes attached to the pedicels.
                                       19 Lemmas faintly 5-veined; awn from the back of the lemma; lower glume longer than the lemma; palea much shorter than the lemma (or absent); [tribe Poeae]
                                       19 Lemmas strongly 3-veined; awn from the tip of the lemma; lower glume shorter than (rarely equaling) the lemma; palea about equaling the lemma; [tribe Cynodonteae; subtribe Muhlenbergiinae]

Key to Poaceae, Key M: grasses with 2+ florets, these exceeded and usually concealed by the glumes

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1 Spikelets disarticulating below the glumes, the spikelets falling as a whole or in clusters; [tribe Poeae]
1 Spikelets disarticulating above the glumes, the glumes remaining attached to the pedicel.
  2 Spikelets dimorphic, paired, each pair consisting of a lower spikelet with sterile florets and an upper spikelet one with fertile florets; [tribe Poeae]
  2 Spikelets monomorphic.
    3 Spikelets each with 1 fertile (bisexual) floret, with 1-several sterile florets, either towards the base or towards the tip of the spikelet.
      4 Fertile floret basal, with 1-several sterile florets towards the tip of the spikelet; [tribe Cynodonteae; subtribe “incertae sedis”]
      4 Fertile floret terminal, with 1-several sterile florets towards the base of the spikelet (the sterile florets sometimes knoblike or like tufts of hairs, and not obviously like florets); [tribe Poeae].
        5 Spikelets with 2 florets, the lower floret staminate and of similar size as the upper, pistillate or bisexual floret; lemma of the lower floret awned; lemma of the upper floret unawned or awned
        5 Spikelets with 2-3 florets, the lower 1-2 florets staminate or sterile, either highly reduced to knobs or tufts of hairs, or shorter than to longer than the terminal, bisexual floret; lemma of the lower florets either awned or unawned; lemma of the upper floret unawned.
          6 Lower sterile florets 2, shorter than to exceeding the bisexual floret; fresh leaves with sweet vanilla odor when crushed; lemma of the lower florets awned or unawned
             7 Glumes unequal, the lower shorter than the upper; lowest 2 florets sterile.
             7 Glumes subequal; lowest 2 florets staminate.
          6 Lower sterile florets 1-2, either highly reduced to knobs or tufts of hairs, or consisting of linear to lanceolate lemmas up to ¾ as long as the bisexual floret; all lemmas unawned
    3 Spikelets each with 2 or more fertile florets.
               8 Spikelets 18-50 mm long; glumes 9-11-veined; [tribe Poeae]
               8 Spikelets 2.5-20 mm long; glumes 1-7-veined.
                 9 Lemma awns apical or dorsal (arising from the apex or back of the lemma or sometimes the midvein prolonged into a 1 mm awn).
                   10 Spikelets 7-20 mm long, with 3-12 florets; ligule of hairs; lemma awn 5-15 mm long; [collectively widespread in our area]; [tribe Danthoniae]
                   10 Spikelets 2.5-7.5 mm long, with 2-3(-4) florets; ligule membranous, sometimes ciliolate but not only consisting of hairs, 0.5-4 mm long; lemma awn 1-9 mm long; [tribe Poeae]
                     11 Awns of the lemmas 1 mm long, essentially a minute prolonged extension of the lemma midvein; lemma apices acute
                     11 Awns of the lemmas 2-8 mm long (therefore conspicuous and not merely a minute midvein extension), bent or geniculate and often basally-twisted and exceeding lemma apices; lemma apices bifid or bicuspidate.
                       12 Panicle branches densely pubescent, usually glistening yellowish-brown or yellowish to tan; panicles either 1-5 cm (Trisetum aureum) OR 5-20 cm long (Trisetum flavescens); leaves evenly distributed; ligules 0.5-1(2) mm, obtuse, lacerate, sometimes ciliolate; plants sometimes with rhizomes to 7 cm long (T. flavescens); [occurring very sporadically in disturbed sites throughout our area or as a ballast waif in NJ]
                       12 Panicles branches glabrous or sparsely pubescent, usually silvery-shiny; panicles (5)20-30(50) cm long; leaves mostly basal or evenly distributed; ligules 0.5-4 mm, truncate or rounded; plants not rhizomatous; [a native of cool, moist, undisturbed northern sites; rare and disjunct in high elevation areas s. to VA]
                 9 Lemma awns basal (arising from the lower half of the lemma); [tribe Poeae].
                          13 Awns geniculate and articulated near the middle joint with a ring of minute conical protuberances, the distal segment of the lemma clavate and differing in shape from the proximal lemma segment; [NJ and PA northward]
                          13 Awns straight or geniculate (sometimes only slightly so), if geniculate then the awn not bearing a distinct ring at the joint and not bearing a clavate distal segment; [collectively widespread].
                            14 Rachilla glabrous, not prolonged beyond the upper floret; spikelets 1.7-3.8 mm long
                            14 Rachilla hairy, prolonged beyond the upper floret as a bristle; spikelets 2.5-7 mm long
                              15 Lemma awn 4-8 mm long, geniculate, exserted beyond the tips of the glumes; lemmas minutely scabrous, dull; leaf blades involute, appearing filiform (rounded in cross-section); ligule 0.5-3 (-5) mm long
                              15 Lemma awn 2-3 mm long, straight or nearly so, scarcely (or not at all) exserted beyond the tips of the glumes; lemmas smooth, shiny; leaf blades flat or folded at the midvein (V-shaped in cross-section); ligule 3-10 (-17) mm long

Key to Poaceae, Key N: grasses with 2+ florets, these readily visible by extending past the glumes

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1 Plants dioecious; plants strongly rhizomatous-clonal; [plants of saline situations, coastal or more rarely inland]; [tribe Cynodonteae; subtribe Monanthochloinae]
1 Plants bisexual; plants cespitose or weakly short- rhizomatous; [plants of various habitats, including saline].
  2 Lemmas 1-3-nerved, the nerves strong and obvious; spikelets 1-27 mm long.
    3 Lemma nerves hairy; lemmas slightly to strongly 2-lobed, the midnerve shortly excurrent between the 2 lobes; [tribe Cynodonteae; subtribe Tridentinae].
      4 Palea glabrous or with hairs < 0.5 mm long; plants perennial; inflorescences exserted, conspicuous
      4 Palea long-ciliate on the upper half, the hairs 0.5-2 mm long; plants annual; inflorescences often largely hidden in the upper sheath
    3 Lemma nerves glabrous; lemmas not at all lobed.
        5 Mature spikelets stiff; grains protruding, with a bottle-neck-like beak; [tribe Diarrheneae]
        5 Mature spikelets not stiff; grains neither protruding, nor shaped with a bottleneck-like beak.
          6 Inflorescence branches usually strongly ascendant (sometimes weakly spreading); culms often disarticulating at the first node; [tribe Arundineae]
          6 Inflorescence branches ascending, widely divergent, or nodding; culms not disarticulating at the first node; [collectively widespread, dry to wet sites]
             7 Florets 3-34 per spikelet; lemmas unawned; [tribe Eragrostideae; subtribe Eragrostidinae]
             7 Florets 2-3 per spikelet; lemmas awned or unawned; [tribe Poeae]
  2 Lemmas 5-many-nerved, the nerves often obscure; spikelets 2-70 mm long.
               8 Sheaths united for at least ½ their length.
                 9 Spikelets in dense one-sided clusters on a few stiff branches; spikelets strongly flattened; [tribe Poeae]
                 9 Spikelets in open or somewhat congested panicles, not as above; spikelets slightly to not at all flattened.
                     11 Callus of the lemma glabrous; [collectively widespread]; [tribe Bromeae]
                     11 Callus of the lemma pubescent; [of VA, WV, KY, and northward]; [tribe Meliceae]
                       12 Lower glumes 1-veined; [plants of wetlands]
                       12 Lower glumes 3-7-veined; [plants of mesic to dry habitats]
               8 Sheaths completely free or united at most up to ½ their length.
                            14 Ligule membranous (the membrane apex ciliate); lower 1-4 florets sterile; disarticulation above the glumes and between the florets; [of various, usually moist, habitats, collectively widespread]; [tribe Centotheceae]
                            14 Ligule of hairs; lower 2-8 florets sterile; disarticulation below the glumes (the spikelet falling whole); [of coastal dunes, from se. VA southward and westward]; [tribe Eragrostideae; subtribe Uniolinae]
                          13 Lowermost florets of the spikelet fertile; [tribe Poeae].
                              15 Lemmas about as broad as long, spreading at a ca. 90° angle to the rachilla
                                  17 Inflorescence pedicels to 0.5 mm thick (if to 0.8 mm as in Sclerochloa dura then culms usually prostrate and leaves also exceeding inflorescence length); panicle branches flexible; lemmas hardened or membranous but not coriaceous at maturity.
                                    18 Inflorescences usually exceeded by the leaves (or sometimes similar in length); culms usually prostrate or procumbent (occasionally ascending); plants often compact and low-growing; mature lemmas hardened
                                    18 Inflorescences exceeding the leaves; culms usually erect; plants compact or not; mature lemmas membranous
                                       19 Lemmas obscurely (3-) 5 (-7) nerved; spikelets 2.5-13 mm long; [habitats usually saline or alkaline]
                                       19 Lemmas prominently 5-9-nerved; spikelets 3.6-6.5 mm long; [habitats non-saline]
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