Vascular Plants of Wisconsin

Comparison of Leymus arenarius and Elymus lanceolatus
Two roughly similar grasses on the Wisconsin shores of Lake Michigan
see text below for full author citations for these species

Leymus arenarius
plants plants plant inflorescence leaf spikelet
population plant plant
blue/green leaves are Leymus--green leaves are Ammophila breviligulata
(a spike)
leaves spikelet
Elymus lanceolatus
plants plants plants inflorescence leaf spikelet
population plant plant inflorescence
(a spike)
(color of leaves is due to dried voucher)

This page is intended to help field workers distinguish between these two grasses so that the invasive alien species Leymus arenarius may be controlled without accidentally doing harm to the rare native Elymus lanceolatus which grows in the same habitat along the Lake Michigan shoreline. It may also provide a little clarity to somewhat confusing nomenclature of these species.

Elymus lanceolatus (thick-spike wheat grass) is native in the U.S.A., widespread in the western United States and is disjunct in the Great Lakes region as the subspecies psammophillus, which is listed "threatened" in Wisconsin. It is also apparently present in Wisconsin as subspecies dasystachya which is not awarded protected status in Wisconsin.

It has been my experience that field botanists in Wisconsin commonly rely on several resources to help in the identification of vascular plants. Chief among these are Michigan Flora (Edward Voss, in 3 volumes), the several volumes of the Flora of North America, and two related, but usefully different websites originating from the herbaria at UW-Stevens Point,
and UW-Madison,
( ).
Both websites deliver content from the same dataset derived from the combined label data from those and several other Wisconsin herbaria. I refer to this information as "the Wisconsin database".

At the moment each of these three sources has adopted a different scientific name for thick-spike wheat grass, as follows:

Flora of North America, Vol 24: Elymus lanceolatus subsp. psammophillus (J.M. Gillett & H. Senn) A. Love.
Michigan Flora, Vol. I: Agropyron dasystachyum (Hooker) Scribner var psammophillum (Gillett & Senn) E. Voss.
Wisconsin database: Elytrigia dasystachya (Hook.) A.Löve & D.Löve subsp. psammophila (J.M.Gillett & Senn) Dewey

Leymus arenarius (L.) Hochst. (Lyme grass) is native to Europe and has become an invasive alien species in the U.S. It was previously known as Elymus arenarius L. [Michigan Flora, and others]. It has become established in Wisconsin and is especially troublesome on the Lake Michigan shoreline where it competes with native species, including Elymus lanceolatus.

How to distinguish between Elymus lanceolatus and Leymus arenarius?

Before providing characters to distinguish these two species, I want to add a caution. The correct identification of plants is seldom accomplished reliably if the appropriate dichotomous keys are not employed. While a person familiar with the plants can often make a reliable field identification using only a few characters, the trick lies in familiarity with the flora that automatically applies numerous characters to the plants before the final few are considered. I mention this because there are other species on the beaches and dunes that also are worthy of consideration and the following table will only be effective if the plant in question is one of the two species listed above. For example Ammophila breviligulata Fernald (dune grass; beach grass) is also present in the same habitats and is similar in size and general aspect to Leymus arenarius. The spike is roughly similar (although the flowers are much different), but the leaves are green rather than blue/green (see the third photo under Leymus arenarius, in which both species are present . Also we should be alert for another threatened grass, Calamovilfa longifolia (Hook.) Scribn. var. magna Scribn. & Merr. on the same beaches. The inflorescence is a panicle rather than a spike and can easily be recognized, but if the plants are sterile the leaves can be fully as wide as those of Leymus arenarius. The bottom line is that it would be best to get someone who is familiar with the various beach grasses to look at any plants in question, until sufficient confidence has been gained.

The following comments will help distinguish between Elymus lanceolatus and Leymus arenarius. Both Elymus lanceolatus and Leymus arenarius are roughly similar in appearance, with strongly glaucus, blue/green leaves. Leymus arenarius is generally a more robust plant, but there is some overlap in vegetative characters.

The best way to separate the two species is by the inflorescence. If the plants are fertile, and they often are, Leymus arenarius spikes (all flowers on a culm are in one spike at the tip, in both species) are 15-25 mm thick and spikes of Elymus lanceolatus are 5-10 mm thick.  That is a very conspicuous difference and the two species can usually be told apart easily once you have seen both in the field. 

For those familiar with grasses and willing to employ floral characters, the two species can be distinguished as follows. Data are taken from the Flora of North America, Vol 24.

  Elymus lanceolatus Leymus arenarius
spike thickness (mm) 5-10 15-25
# of spikelets per node of the spike 1 2
lemma length (mm) 7-12 12-25
lemma hairs many longer than 1 mm 0.3-0.7 mm long
anther length (mm) 3-6 6-9
leaf blade width (mm) 1.5-6.0 3-11

If there are no fertile plants available, the leaves of Leymus arenarius are generally broader than those of Elymus lanceolatus. Leymus arenarius leaf blades are 3-11 mm wide and leaves of Elymus lanceolatus 1.5-6 mm wide. There is overlap from 3 to 6 mm, but if plants have most leaves wider than 6 mm and some wider than 8 mm you can reject the possibility that the plant is Elymus lanceolatus..

wis mcap
known distribution based on vouchers


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