Leersia oryzoides (Rice Cutgrass)

Plant Info
Also known as:
Genus:Leersia
Family:Poaceae (Grass)
Life cycle:perennial
Origin:native
Habitat:part shade, sun; wet; marshes, swamps, shores, banks, wet ditches, shallow water
Fruiting season:August - October
Plant height:2 to 5 feet
Wetland Indicator Status:GP: OBL MW: OBL NCNE: OBL
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

[photo of flowering spikelets] Branching cluster at the top of the stem, pyramidal in outline, 4 to 12 inches long, 1 branch per node near the top and 2 or more branches per node near the base. Often, the lowest branches and/or auxiliary clusters are at least partially enclosed in the uppermost leaf sheaths. Branches are 1½ to 4 inches long, initially erect becoming ascending to spreading, each with 1 to 4 branchlets that are congested on the upper half or so of the branch and remain more or less appressed to the branch. Spikelets (flower clusters) are arranged all on one side of a branchlet, appressed, overlapping for about half their length. Spikelets are short-stalked, elliptic in outline resembling a grain of rice, and have a single floret.

[close-up of branch] A pair of bracts (glumes) at the base of a spikelet is absent altogether. Surrounding a floret are a pair of bracts (lemma and palea), both boat-shaped, whitish with green veins, 4 to 6 mm (1/8 to ¼ inch) long and flattened laterally with conspicuous bristly hairs along the keels, so the spikelet appears fringed all around the outer edge, and also often have scattered hairs on the surfaces. The lemma is about ¾ the width of the spikelet, 5-veined, hairy along the edges like on the keel. The palea is slightly longer than the lemma, about ¼ the width of the spikelet, 3-veined, and occasionally lacks hairs on the keel.

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

[photo of leaves] Leaves are 3 to 12 inches long, 5 to 15 mm (to ~½ inch) wide, spreading to ascending, flat, usually rough textured on both surfaces, and fringed in sharp, stiff hairs around the edges.

[photo of sheath, ligule and node] The sheath is sparsely covered in sharp, stiff hairs, may be short hairy on the back and/or front where it meets the blade, and often has a pair of small triangular lobes (auricles) at the apex. The ligule (membrane where the leaf joins the sheath) is .5 to 1 mm long, inverted U-shaped to straight across, not fringed with hairs, and joined to the sheath auricle. Nodes are densely hairy with downward pointing (retrorse) hairs. Stems are hairless to sparsely rough hairy, unbranched, erect or prostrate from the base then rising near the tip (decumbent) and rooting at the nodes, single or multiple from the base and forming loose clumps. Plants often form colonies from long, scaly rhizomes.

Fruit: Fruit type: seed without plume

[photo of individual spikelets] Spikelets turn light brown at maturity, the florets shedding individually as each grain matures, leaving a naked stem behind. Grains (seeds) are light to dark brown, 2 to 3.5 mm long.

Notes:

Leersia oryzoides is a common wetland species and called “cutgrass” for a reason, as anyone who has has the misfortune of walking through a stand of it will attest. The stiff hairs on leaves and sheaths are very sharp and can cut through unprotected skin—it's drawn my own blood more than once! While from a distance, Leersia oryzoides may resemble a number of other grasses with a loose panicle, a closer inspection of the spikelets shows how different the Leersia species are: the single-flowered spikelets congested at branch tips, lacking awns and flattened laterally, with conspicuous hairs along the keel of both lemma and palea, along with the absence of glumes are a unique combination, and all 3 Minnesota Leersia species also have densely hairy stem nodes. Leersia oryzoides is the most common of the 3, and distinguished from the others by spikelets 4 to 6 mm long, shaped much like a grain of rice, often have hairs on the lemma and palea surfaces as well as the keels, and are overlapping on the branchlet by about half their length. By comparison, Leersia lenticularis (Catchfly Grass), a rare species of floodplain forest, has nearly round spikelets, and Leersia virginica (White Grass) panicles are more sparsely branched, has spikelets less than 4 mm long that do not overlap much, if at all, and usually lacks hairs on lemma and palea surfaces, sometimes also on one or both keels.

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More photos

Photos by K. Chayka taken in Ramsey County. Photos courtesy Peter M. Dziuk taken in Anoka, Chisago, Ramsey and Winona counties.

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