Lolium multiflorum (Annual Ryegrass)

Plant Info
Also known as: Italian Ryegrass
Genus:Lolium
Family:Poaceae (Grass)
Life cycle:annual, short-lived perennial
Origin:Europe
Status:
  • Weedy
Habitat:part shade, sun; disturbed soil; roadsides, lawns, shores, open woods
Fruiting season:July - August
Plant height:1 to 5 feet
Wetland Indicator Status:GP: FACU MW: FACU NCNE: FACU
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: spike

[photo of spikes] A single erect spike to 12 inches long at the tip of the stem, with a single spikelet (flower cluster) at each node, arranged alternately on opposite sides of the stem. Spikelets are stalkless, flattened, appressed to ascending, rotated so the edge of the spikelet is against stem (rachis) rather than the flat side. The rachis is grooved on the side facing the spikelet and rough-textured on the opposite side. Each spikelet is 8 to 31 mm (to 1¼ inch) long (excluding any awns) and has 10 to 20 florets; the uppermost floret may be sterile.

[photo of spikelet] At the base of a spikelet is a single bract (glume) that is leathery, 4 to 7-veined, not keeled, hairless, lance-elliptic, blunt to pointed at the tip, awnless, and shorter than the adjacent floret; only the terminal spikelet has a pair of glumes. Florets are surrounded by a pair of bracts (lemma and palea), the lemma hairless, 5-veined, 5 to 8 mm long, not keeled, with 2 small teeth at the tip and usually a straight awn 5 to 15 mm (to ~½ inch) long arising from between the teeth; the palea is more or less as long as the lemma.

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

[photo of sheath, ligule and node] Leaves are alternate, ascending to spreading, up to 12 inches long, 3 to 10 mm (3/8 inch) wide, flat and hairless. The sheath is hairless and has a pair of whitish to brown lobes (auricles) at the sheath apex. The ligule (membrane where the leaf joins the sheath) is 1 to 2 mm long, straight or jagged across the top edge, and lacks a fringe of hairs. Nodes are hairless. Stems are unbranched, smooth, usually erect, multiple from the base, forming clumps. Leaves of new shoots are rolled in along the edges.

Fruit: Fruit type: seed without plume

[close-up of spikelet] The awns remain straight as spikelets mature, all turning bleached tan when dry. Florets drop off individually at maturity leaving the glumes behind on the stem.

Notes:

Annual Ryegrass is a European introduction that is sometimes planted as a cover crop or for forage. It escapes cultivation, ending up on roadsides, in parking lots, along trail edges and other areas of disturbance, and is likely under-reported in Minnesota. Several years ago we came upon a patch of it in a weedy pile of dirt at Forestville/Mystery Cave State Park, but the area has since been restored and the Lolium vanished.

There are two Lolium species known to be in Minnesota, the other being Lolium perenne (Perennial Ryegrass), and it is not always easy to distinguish them; the two are even considered different vars of the same species in some references (L. perenne var. multiflorum or var. aristatum, and var. perenne). Lolium in general is fairly distinct with the spikelets rotated so the edge is against the stem (rachis) and only the terminal spikelet has two glumes. Vaguely similar are some Elymus species, notably Quackgrass, which has the flat side of spikelets against the stem and a pair of glumes on all spikelets.

L. multiflorum is distinguished by a grooved rachis that is rough-textured, spikelets usually having 10 to 20 florets, the glume shorter than the adjacent floret, most lemmas having a 10 to 15 mm long awn, sheaths with well-developed auricles, and leaves of new shoots with in-rolled edges. By comparison, L. perenne has a rachis that is smooth on the side opposite the spikelet, spikelets have 5 to 10 florets, the glume is about as long as or longer than the adjacent floret, lemmas are awnless or have awns less than 8 mm long, sheaths lack auricles or have just small auricles, and leaves of new shoots are folded lengthwise. A third Lolium species, L. temulentum, is present in Iowa and may also be in MN; it has a particularly long glume, even over-topping the uppermost floret in the spikelet.

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More photos

Photos by Peter M. Dziuk taken in Fillmore County.

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