Poa nemoralis (Wood Bluegrass)

Plant Info
Also known as: Wood Meadowgrass, Sylvan Bluegrass
Genus:Poa
Family:Poaceae (Grass)
Life cycle:perennial
Origin:Europe
Status:
  • Weedy
Habitat:part shade, sun; dry rocky or sandy soil; open woods, forest edges, trail edges, rock crevices, cliffs, creek banks
Fruiting season:June - August
Plant height:12 to 30 inches
Wetland Indicator Status:GP: FACU MW: FACU NCNE: FACU
MN county distribution (click map to enlarge):Minnesota county distribution map

Pick an image for a larger view. See the glossary for icon descriptions.

Detailed Information

Flower: Flower shape: indistinct Cluster type: panicle

[photo of panicle] Panicle 3 to 6 inches long, egg-shaped to pyramidal in outline, usually erect, sometimes slightly nodding, the branches ascending to spreading. Spikelets (flower clusters) are short-stalked, light green sometimes purple-tinged, flattened, oblong to lance-elliptic, 3 to 8 mm (to 1/3 inch) long with 2 to 5 florets; the uppermost floret may be sterile.

[close-up of branch] At the base of a spikelet is a pair of bracts (glumes) that are both narrowly lance to egg-shaped, tapering to a pointed tip, awnless, hairless, light green with transparent whitish edging, 3-veined, rough along the keel, the lower glume 2 to 3 mm long, the upper glume somewhat larger than the lower glume. Surrounding a floret is a pair of bracts (lemma and palea), the lemma 2.4 to 4 mm long, as long as or slightly longer than the upper glume, egg-shaped with transparent whitish edging, 5-veined, the lateral veins not reaching the tip of the lemma, long white hairs on the keel and the 2 edge veins, hairless between them and on the other 2 lateral veins; the palea is nearly as long as the lemma but narrower, 2-veined, rough along the veins. The thickened base of the floret (callus) has sparse, short, crinkled hairs; the stalk between florets (rachilla) is covered in short, straight hairs.

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

[photo of leaves] Leaves are alternate with 3 to 5 leaves widely spaced along most of the stem. Leaves are flat, up to 4 inches long, 1 to 3 mm wide, hairless, boat-shaped at the tip, often arranged perpendicular to the stem and not much reduced in size as they ascend the stem.

[photo of sheath, ligule, node and stem cross-section] The sheath is hairless and the edges are fused for 1/10 to 1/5 their length (closed sheath). The ligule (membrane where the leaf blade joins the sheath) is .2 to .8 mm long and lacks a fringe of hairs. Nodes are smooth and most are exposed. The uppermost node is positioned at half to ¾ the stem length. Stems are unbranched, mostly erect, slightly compressed, multiple from the base forming clumps, and lack rhizomes or stolons.

Fruit: Fruit type: seed without plume

[photo of mature florets and grain] Individual florets drop away when mature, leaving the glumes behind persisting on the stalk. The grain (seed) is golden to brown, about 1.5 mm long.

Notes:

Wood Bluegrass is a cool-season grass introduced from Europe. It has not been recorded many times in Minnesota but is likely under-reported due to its similarities with other grasses; it is considered potentially invasive in Wisconsin. It's been found in forest clearings, along trail edges, and in rock crevices of cliffs and rocky shores and banks.

Wood Bluegrass is recognized by its clump-forming growth, uppermost node around 2/3 the length of the stem (measured from the ground to the base of the panicle), stem leaves all near the same size and often perpendicular to the stem especially when young (though may become ascending with age), ligule usually about .5 mm long, upper glume about as long as the lowest lemma on the spikelet, lemmas long hairy along the keel and the 2 marginal veins, hairless between the veins, and hairy rachillas (strong magnification required to see).

Poa nemoralis closely resembles two native Bluegrasses, and all three may be found in similar habitats: Poa glauca (Glaucus Bluegrass) and Poa interior (Inland Bluegrass), both of which have the uppermost node below the middle of the stem and ligules usually at least 1 mm long.

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More photos

Photos by K. Chayka taken in the yard. Photos by Peter M. Dziuk taken in Lake, Pine and Ramsey counties, and his yard.

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