Leymus mollis is a species of grass known by the common names American dune grass, American dune wild-rye, sea lyme-grass, strand-wheat, and strand grass. Its Japanese name is hamaninniku. It is native to Asia, where it occurs in Japan, China, Korea, and Russia, and northern parts of North America, where it occurs across Canada and the northern United States, as well as Greenland. It can also be found in Iceland.

This is a rhizomatous perennial grass with erect stems growing up to 1.7 meters tall. The leaf blades can be nearly a meter long in ssp. mollis, and up to 1.5 centimeters wide. The flower spike is up to 34 centimeters long by 2 wide. Each spikelet may be up to 3.4 centimeters long and contain up to six florets. There are two subspecies. Subspecies villosissimus is mostly limited to arctic regions, and is mainly coastal. It is usually a smaller plant than ssp. mollis. The two subspecies are otherwise hard to tell apart, even when growing sympatrically. The most reliable character to use to distinguish them is the type of hairs on the glumes and lemmas; ssp. villosissimus has long, soft, sometimes shaggy hairs (villous), while ssp. mollis has fine, thin hairs (pilose), and generally fewer of them. There is no awn.

This grass usually grows in coastal habitat, especially on dunes. It can be an important part of dune ecology. The grass usually grows on the foredune and on embryo dunes, less often on the backdune. It is one of the first plants to establish in the process of ecological succession in the early stages of the development of a sand dune. In these loose dunes facing the ocean the plants tolerate salt spray, salty sand, little to no fresh water, unstable substrates, occasional inundation during storms, low nutrient levels, and abrasion by wind, water, and ice storms. Seedlings may become buried. This type of environment causes stress in a plant. The grass grows from a large rhizome that anchors it into shifting and unstable sands. When there are many plants on a dune, their rhizomes form a network that helps to stabilize it, preventing erosion. The network becomes "the skeleton of the foredune." This makes the grass a valuable species for landscape rehabilitation in native beach habitat.

Other plants that occur with the grass include Lathyrus japonicus, Achillea millefolium, Festuca rubra, Ammophila breviligulata, Rhus typhina, Rosa rugosa, and Arctanthemum arcticum. It also grows with mosses such as Pleurozium shreberi and Polytrichum spp. and lichens such as Cladina spp. It was observed to be one of the most common plants in the arctic nesting sites of the snow goose. It is thought that the geese prefer the overall ecosystem that hosts the grass, rather than favoring the grass itself.

Leymus mollis has been studied for possible usage in the science of wheat breeding. Wide hybridization of wheat and L. mollis has been conducted successfully since the 1960s to generate many hybrids. An important example of L. mollis hybridization with wheat occurred when the AD99 L. mollis line was hybridized with wheat. The AD99 was resistant to powdery mildew, and the resultant wheat hybrid yielded six lines that were also resistant to powdery mildew. This experiment can be used as a basis for L. mollis to be considered as a very useful genetic resource. By using Expressed Sequence Tags (ESTs) it was found that wheat has a complex and redundant genome. ESTs serve to identify transcribed parts of the genome. Through a comparative study it was found that L. mollis has some of these genes as well; because they are highly conserved. These genes are more prominent in L. mollis than wheat however, and are used for osmotic and drought stress tolerance. Due to their similarity though, they have the ability to be hybridized into wheat. Overall these ESTs help to provide proper tools for molecular markers to help identify possible introgression of genes into wheat, particularly in regards to osmotic stress tolerance.

Leymus mollis' relative success with wheat breeding can be demonstrated specifically by utilizing the Genetic In-Situ Hybridization (GISH) method. Comparative GISH showed that the genomes in the genus Leymus are fairly diverse. However, it was also found that chromosomes of species within this genus were able to undergo complete meiotic paring in hybridism with each other. Using the GISH technique, it was found that differences in sub-telomeric heterochromatin do not affect meiotic pairing. Because of this it can be understood that the differences between Leymus genus and Triticum (wheat) would not prevent successful hybridization. This conclusion results from the fact that Leymus is already able to overcome differences within its own genus in pairing.

Leymus mollis is generally looked at for hybridization due to it being highly adaptable and robust. To determine this adaptable nature of L. mollis, its seedlings were studied in an environment in which there was low nutrient availability. In this environment, the seedlings were very tolerant of the low nutrients and were still able to sprout. Generally, low soil moisture is considered to be an important mortality factor, yet L. mollis seedlings were able to survive successfully. The period of drought that these seedlings were tested in was 5 successive days, and L. mollis had a survival rate of 93%. This adaptability of the plant is something that is not seen in wheat seedlings, which is why it is looked at for hybridization. Being a dune grass, L. mollis also has an extensive ability to survive salinity. The viability of these seeds in the salinity was found to be higher than fifty percent following submergence for seven days. This is translatable to L. mollis being able to grow in soil with high salt content. The surrounding soil may not be viable for traditional plants, however L. mollis still retains the ability to grow. This further demonstrates the wide adaptability of L. mollis.

As a result of strong anthropogenic pressures in today’s world, one response is to look at sustainable development of our vegetative environment. Biologists are continuously looking for new ways to combat these artificial pressures, and one of the species that has potential to be more closely looked at is Leymus mollis, an extremely adaptable plant species. Specific traits of L. mollis can be proven beneficial in the hybridization and domestication of this species or a hybrid species. These traits include the species’ ability to tolerate moderate burial intensity and sustain trampling, adapt to drought and water deficiency, resist many fungal diseases such as wheat stripe rust, contain high rhizome bud viability, and tolerate salt and various diseases.