Ammophila breviligulata (American Beach Grass)

Plant Info
Also known as:
Family:Poaceae (Grass)
Life cycle:perennial
  • State Threatened
Habitat:sun; dry sandy soil; dunes, shores
Fruiting season:August - September
Plant height:20 to 40 inches
Wetland Indicator Status:GP: none MW: UPL NCNE: UPL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: indistinct Cluster type: panicle Cluster type: spike

[photo of spike-like panicles] Spike-like branching cluster at the top of the stem, 6 to 16 inches long, the branches appressed and the panicle usually straight, sometimes slightly nodding. Spikelets (flower clusters) are short-stalked, overlapping and tightly crowded, 10 to 15 mm (to ~½ inch) long, narrowly lance-elliptic in outline with a single floret.

[photo of panicle branches and floret] At the base of a spikelet is a pair of bracts (glumes) that are narrowly lance-elliptic with a pointed tip, the upper glume 9 to 15 mm (to ~½ inch) long and 3-veined, the lower glume about as long or slightly shorter and 1-veined. Florets are surrounded by a pair of bracts (lemma and palea), the lemma 8 to 14 mm long, usually slightly shorter than the glumes, pointed at the tip, awnless, weakly 5-veined, rough-textured; the palea is slightly shorter and 2 to 4-veined. The thickened base of the floret (callus) is densely covered in white hairs 1 to 3 mm long that are hidden by the glumes.

Leaves and stems: Leaf attachment: alternate Leaf attachment: basal Leaf type: simple

[photo of sheath and ligule] Leaves are mostly near the base, 8 to 24 inches long, the edges usually rolled in (involute), 4 to 8 mm (to ~1/3 inch) wide when flat, hairless, stiff, rough textured on the upper surface, and gradually taper to a thread-like tip. The sheath is hairless. The ligule (membrane where the leaf joins the sheath) is convex to straight across the top edge, 1 to 3 mm long and lacks a fringe of hairs. Nodes are smooth.

[photo of vegetative leaf clumps] Stems are hairless, unbranched, mostly erect, multiple from the base forming dense clumps. Plants form large colonies from long rhizomes, a mix of vegetative and flowering plants.

Fruit: Fruit type: seed without plume

[photo of mature glumes and florets] Spikelets are straw-colored at maturity, the florets dropping off leaving the glumes behind on the stalk.


American Beach Grass is one of the rarest native grasses in Minnesota, known only from Minnesota Point in St. Louis County, where it reaches the western edge of its natural range; it was introduced to the Pacific Coast of North America in the 1930s, where it has become invasive, negatively altering fragile coastal beach habitats. Sad. According to the DNR, Minnesota Point is part of one of the longest freshwater sandbars in the world, stretching from Duluth to Superior, Wisconsin, and is the only suitable habitat for this species in Minnesota, but the dunes on much of the Point have been severely degraded or destroyed by development. A strain of this species from Michigan was introduced in parts of the Point to help stabilize the dunes but it is not yet known what effect, if any, it will have on what remains of the native population. Ammophila breviligulata was listed as a Threatened species in 1984.

A. breviligulata is recognized by the long and usually straight spike-like panicle, the branches appressed; spikelets 10 to 15 mm long, crowded, awnless and single-flowered; glumes nearly equal in length, florets with callus hairs 1 to 3 mm long; hairless sheaths, ligules and nodes; leaves mostly involute (rolled in). It is both clump-forming and colony-forming and can cover large areas. There are 2 subspecies, though these are not universally recognized; subsp. breviligulata, present along the Atlantic coast, St. Lawrence River Valley and shores of the Great Lakes, is as described above and blooms late July to September; subsp. champlainensis, present in New England, is overall smaller with shorter leaves, panicles and slightly shorter spikelets, though there is significant overlap, and blooms June to mid-July.

In Minnesota, most similar is the much more common Sand Reed Grass (Calamovilfa longifolia), which can reach heights of 7+ feet, has a slightly more open and less dense panicle, shorter spikelets (less than 9 mm long), distinctly unequal glumes, callus hairs half or more as long as the lemma, and ligules fringed with hairs. American Beach Grass has been known to hybridize with Canada Bluejoint (Calamagrostis canadensis), the hybrid having intermediate characteristics; the hybrid has not been recorded in Minnesota.

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More photos

Photos by K. Chayka and Peter M. Dziuk taken on Minnesota Point, St. Louis County.


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