Key to Common Maine Grasses

This is an alternate key to genera for Grasses and Rushes of Maine based on spikelet arrangement. Statements are designed to be read in order. If your grass doesn't match the first statement, go to the next group or statement. Additional notes at the page bottom.

GROUP KEYS

1 - Unisexual spikelets; staminate and pistillate flowers on separate parts of the panicle - WILD RICE GROUP

2 - Spikelet of a single floret flattened laterally; glumes lacking; palea & lemma same length; mid nerves ciliate; leaves scabrous on both surfaces and margins; culm nodes with white hairs - CUTGRASS GROUP

3 - Inflorescence a panicle of 1-sided spike-like branches; laterally compressed spikelets; 1 floret per spikelet; rhizomatous - CORDGRASS GROUP

4 - Inflorescence an articulated raceme; 2 spikelets at each joint, the fertile spikelet sessile & the sterile spikelet pedicelled - BLUESTEM GROUP

5 - Inflorescence a bilaterally symmetrical spike; spikelets with florets in clusters of 2 or more; some florets sterile - BARLEY GROUP

6 - Spikelet with at least 2 florets; at least 1 glume as long as, but often longer than, the lowest lemma - OATS GROUP

7 - Two or more fertile florets; both glumes shorter than first lemma; awns terminal or absent - BLUEGRASS GROUP

8 - One apparent fertile floret, lower glume much reduced or absent; fertile floret with hardened lemma & palea as compared to glume - PANIC GRASS GROUP

9 - Spikelet with single floret with awned lemma; no sterile florets - BENTGRASS GROUP

GENUS KEYS

1 - WILD RICE GROUP

A - Zizania aquatica, Z.palustris

B - Zea mays

2 - CUTGRASS GROUP

Leersia oryzoides, L.virginica

3 - CORDGRASS GROUP

Spartina alternaflora, S.patens, S.pectinata

4 - BLUESTEM GROUP

A - Racemes multiple on each peduncle; digitate inflorescence = Andropogon gerardii

B - Racemes single on each peduncle; prominent white hairs around the spikelets = Schizachyrium scoparium

5 - BARLEY GROUP

A - Spikelets attached to spike on edge = Lolium multiflorum, L.perenne

B - Coastal sandy habitats; inflorescence a stout spike; 2 spikelets per node; 3-5 florets per spikelet; glumes & lemmas densely hairy = Leymus mollis

C - Spikelets attached to spike on broad face; salt marshes & coastal beaches; leaves bluish white less than 6 mm wide; glumes unawned = Thinopyrum pycnanthum

D - Spikelets attached to spike on broad face; glumes & lemmas usually long awned = Elymus repens, E.trachycaulus, E.virginicus (+5)

E - 3 spikelets at each node; 2 florets sterile; glumes hairy; glumes & lemmas awned; ligules with auricles = Hordeum jubatum, H.vulgare (barley)

F - 4 sided spike; glumes 1 veined, hairless; glumes & lemmas awned; lemmas stiff and ciliate on midrib & margins = Secale cereale (rye)

G - Lemmas not ciliate Triticum aestivum (wheat)

6 - OATS GROUP

A - Glumes 15 mm or longer; spikelets pendulous = Avena sativa (oats)

B - Inflorescence a sparse panicle; upland species; awns twisted & bent arising between 2 teeth at the apex of the lemma; glumes keeled; cespitose = Danthonia compressa, D.spicata

C - Two florets, the lowest floret staminate; awned from lower third of the lemma; awn twisted, bent and 10 mm or longer; inflorescence an open panicle = Arrenatherum elatius

D - Two perfect florets; awned below middle = Deschampsia flexuosa, D.anadyrensis, D.caespitosa,

E - Glumes significantly unequal in length; inflorescence a spike-like panicle; upland species = Anthoxanthum odoratum, A.ovatum

F - Glumes subequal in length and barely longer than floret; 1 perfect & 2 staminate florets; inflorescence an open panicle; formerly genus Hierochloe = Anthoxanthum nitens, A.hirtum, A.monticola

G - Inflorescence a spikelike panicle; lemmas with 2 teeth; awn basally twisted and arising from upper third of lemma = Trisetum spicatum

7 - BLUEGRASS GROUP

8 - PANIC GRASS GROUP

A - Inflorescence multiple one sided digitate spikes = Digitaria ischaemum, D.sanguinalis

B - Distinctly awned = Echinochloa crus-galli, E.muricata, E.walterii

C - Inflorescence a spike; florets with numerous long subtending bristles = Setaria pumila, S.faberi, S.italica, S.verticillata, S.viridis

D - Inflorescence a well-developed panicle; basal leaves lanceolate to ovate & different from stem leaves = Dichanthelium acuminatum, D.boreale, D.clandestinum, D.depauperatum, D.latifolium, D.linearifolium (+4)

E - Inflorescence a well-developed panicle; basal leaves linear to lanceolate & usually similar to the stem leaves; Leaf sheaths terete = Panicum capillare, P.virgatum (+3)

F - Plant of wet habitats; inflorescence a unique open panicle with some branches ascending, others descending = Sorengia longifolia

G - Floret encased in a modified fasicle of spikes - Cenchrus longispinus, C.spinifex

9 - BENTGRASS GROUP

A - Inflorescence spike-like; spikelet laterally compressed; glumes lacking awns and about as long as lemma = Alopecurus pratensis (+2)

B - Inflorescence robust spike-like to 30 cm long; large, cespitose, dune species = Ammophila breviligulata

C - Inflorescence a spikelike panicle; spikelet laterally compressed; glumes awned; lemmas awnless & shorter than the glumes = Phleum pratense, P.alpinum

D - Inflorescence a sparse contracted panicle; UPL woodland species = Oryzopsis asperfolia

E - Lemmas long awned, up to 3X length of lemma; FACW woodland species = Brachyelytrum aristosum

F - 3 twisted awns = Aristida (3).

G - Inflorescence a panicle; large grass; lemma shorter than glumes and with short awn; callus of copious straight hairs = Calamagrostis canadensis (+3)

H - Spikelet with 2 tufts of hairs; closed panicle sometimes appearing spikelike = Phalaris arundiacea, P.canariensis

I - Stipitate florets (above glumes); FACW woodland species = Cinna latifolia, C.arundinacea

J - Lemma longer than glumes; awns apically attached; nearly all with a narrow compact inflorescence; bearded callus = Muhlenbergia frondosa, M.glomerata, M.mexicana, M.sylvatica (+6)

K - Open panicle; glumes sharp pointed, with scabrous keel, & at least as long as lemmas = Agrostis capillaris, A.gigantea, A.perennans, A.scabra, A.stolonifera (+5)

L - Inflorescence partly covered by leaf sheath; ligule of hairs; upland habitats = Sporobolus vaginiflorus (+3)

M - Inflorescence a sparse panicle; long awned; UPL = Piptatherum pugens, P.racemosa, P.canadense

Usage Notes

Read each group, in order, until you come to one that describes your mystery grass. Then do the same for the lettered statements - read each statement in the order presented. More charismatic genera or more common genera are listed first. That helps speed ID and decrease frustration.

At that point you have the genus. If it is a monospecific genus you're done. Otherwise look for the genus in Grasses and Rushes of Maine (GROM) or GoBotany or Grasses of the Northeast by Magee or Flora Novae Angliae by Haines. This key does work with Hitchcock's 2 volume Manual of the Grasses of the US but those volumes include all species in the US and the taxonomy is outdated. Hitchcock is however exceptionally inexpensive.

The species in bold are very common in Maine. You may find you can recognize the species in bold on sight in only a few summers. Species in italics are less common. Species in red are listed as species of concern in Maine. Consult the State website for details.

If there are 4 or more species in a genus, the most common and widespread species are the ones listed, with the number of additional species is noted in parentheses.

A few genera that haven't been seen in 20 or more years have been omitted as have rare genera. Some new species are turning up in Maine. The GoBotany addenda has those but only the most fervid Poaceae enthusiasts are likely to encounter them.

The Checklist of Maine Grasses also on this website has the species wetland status and anthesis timing. Both can be helpful in identifications.

Some species require a dissecting microscope and micro measurements for identification. I have found AmScope to be a quality source for microscopes of reasonable price.

This key is helpful for much of New England, but as one moves away from Maine, especially south, additional genera and species occur. Some of those are fairly common making this key less useful.

Why Does This Key Exist?

I like the keys that were developed for Grasses and Rushes of Maine (GROM). They begin as an easy to comprehend chart that quickly get you to a manageable shorter dichotomous key. They work very well and are easy to use. I highly recommend the book for both its keys and its excellent photos.

While the keys are great for getting an ID, I don't think they actually allow people to learn grasses. Traditionally grass identification was done by keying a specimen to one of 13 Tribes. Those Tribes were based on (mostly) easily recognizable morphological characteristics. With some practice, experience, and having learned to recognize some of the common species in an area, one could often assign a specimen to a Tribe in the field quickly. In some cases the genus was readily apparent without cracking the key. This meant keying became much easier and mistakes less time consuming.

Traditional taxonomists and creators of keys require couplets to key to a taxonomic group. Even if one species was morphologically distinct, the key had to key to every genus once and only once. That's how one learned the taxonomy which was considered part of using a key.

Fortunately common sense has been creeping in for the past 2 decades. Now many keys, particularly those designed for field use like GROM, are no longer that strict. By allowing a genus to appear in multiple places in the key and basing the couplets on more macroscopic morphological characteristics (vs requiring X20 plus magnification) - keys have become more user friendly.

This is where modern species definitions based on laboratory analysis versus visual characteristics come into play. These new and inexpensive techniques have thrown taxonomy on its head with well known species being moved to different Tribes and genera to ensure monophylly. (Grasses, so far, have been spared changes to Family.) This means all traditional taxonomic keys are invalid with new Tribes being named and several being retired. New keys have been generated.

This is tolerable for those of us that already know many grasses but extremely challenging for the novice. But since the older Tribes are now defined differently, I have no problem using them in a modified fashion for this key. I have termed them "groups" that are not taxonomically valid. My groups are based solely on visible morphology. I've moved some genera or species groups to a group different than the traditional Tribe based on easily recognizable characteristics. It isn't perfect but it works well for the novice and allows them to more easily categorize grasses they find.

I'm sure both purists and taxonomists will have some issues with this. However, the goal for this key is to provide a method to identification for those new to grasses - tradition and taxonomy be damned. I have been using this key in the field with great success for several years with Magee and with Hitchcock instead of GROM. GROM makes this key even more useful. The results with new students of grasses have also been excellent.

While this key does not work for every species in Maine and purposely ignores rare genera and species, it works for species I've encountered in the field. And unlike the book, having it on my phone or tablet adds no weight to my pack. Pulling up photos from GoBotany in the field means I can get a quick visual common sense check - hence the link on the page. If the photo doesn't match or the key fails, I can collect a stalk and key it at home with the book and a dissecting scope.

If you are new to grasses, I hope you give this key a shot. And also consider attending one of my workshops at a land trust near you in Maine or attending a seminar, virtual or in person, at Eagle Hill Institute in Steuben Maine.

Thanks to Dennis Magee for his many suggestions and corrections. Remaining issues are mine.

Errors, improvements or suggestions? Email Jeff at info@DigitalNaturalist.info.

last updated 2022-Aug-15