Poa compressa (Canada Bluegrass)

Plant Info
Also known as: Flat-stem Bluegrass
Genus:Poa
Family:Poaceae (Grass)
Life cycle:perennial
Origin:Europe, Asia
Status:
  • Weedy
Habitat:part shade, sun; dry to moist disturbed soil; roadsides, fields, prairies, waste places, open woods, shores, rocks, gravel pits
Fruiting season:July - September
Plant height:4 to 24 inches
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: panicle

[photo of panicle] Panicle to 4 inches long, rather longer than wide, the short branches usually ascending, sometimes erect, less often spreading. Spikelets (flower clusters) are short-stalked, light green often purple-tinged, flattened, oblong to egg-shaped, 3 to 7 mm (to ~¼ inch) long with 3 to 7 florets; the uppermost 1 or 2 florets may be sterile.

[close-up of spikelets] At the base of a spikelet is a pair of bracts (glumes) that are both lance to egg-shaped, hairless, awnless, keeled, 3-veined, light green with transparent whitish edging near the tip, 2 to 3 mm long, the lower glume as long as or slightly shorter than the upper glume. Surrounding a floret is a pair of bracts (lemma and palea), the lemma 2.5 to 3.5 mm long, blunt to pointed at the tip, thin and whitish on the edges near the tip, keeled with 4 obscure lateral veins that do not reach the tip of the lemma, sparse white hairs on the veins near the base; the palea is slightly shorter than the lemma, 2-veined. The thickened base of the floret (callus) may or may not have a few long, crinkled hairs.

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

[photo of twisted leaf] Leaves are alternate and basal, floppy, up to 4 inches long, 1 to 4 mm wide, hairless, boat-shaped at the tip, flat or folded, and may be spirally twisted in the middle of the blade. Color is blue-green.

[photo of stem cross-section, sheath, ligule, and node] The sheath is hairless, compressed, keeled along the back, and the edges fused on the lower 1/10 to 1/5 (closed sheath). The ligule (membrane where the leaf blade joins the sheath) is up to 3 mm long, straight across to convex along the edge, and lacks a fringe of hairs. Nodes are smooth and elliptic in cross-section. Stems are distinctly flattened, unbranched, usually single from the base, erect to ascending or prostrate from the base and rising at a lower node (geniculate). Plants form colonies from spreading rhizomes, sometimes in loose clumps.

Fruit: Fruit type: seed without plume

[photo of immature and mature florets] Spikelets turn light brown with maturity, the individual florets dropping away leaving the glumes behind persisting on the stalk. The grain (seed) is amber brown, about 1.5 mm long.

Notes:

Canada Bluegrass is a cool-season grass introduced from Europe or Asia (not Canada) and is one of the most common grasses in North America, present throughout Canada and every US state except Florida. It's been used both for forage and erosion control, and readily escapes into other areas of disturbance, such as roadsides, fields, woodland edges, and gravel pits. It is not an uncommon sight on the rocky north shore of Lake Superior.

Canada Bluegrass is most easily recognized by its colony-forming habit; flattened stems; blue-green leaves with boat-shaped tips and may be spirally twisted near the middle; sheaths compressed and keeled; spikelets with 3 to 7 florets, lemmas to 3 mm long usually with sparse hairs on the lower half of major veins. The callus may or may not have a few cobwebby hairs.

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More photos

Photos by Peter M. Dziuk taken in Cook, Dakota and Ramsey counties.

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