Poa glauca (Glaucous Bluegrass)
|Also known as:||Pale Bluegrass|
|Habitat:||part shade, sun; average to dry; cliffs, rocky banks, talus slopes, rock outcrops|
|Fruiting season:||July - August|
|Plant height:||4 to 16 inches|
|Wetland Indicator Status:||none|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Panicle up to 4(8) inches (3.5 to 10+ cm) long, narrowly lance to egg-shaped in outline, erect, the short branches mostly ascending at flowering time, often becoming more erect with maturity; there are usually 2 or 3 branches per node but may be as many as 5. Spikelets (flower clusters) are short-stalked, often purple-tinged, flattened, oblong to lance-elliptic, 3 to 7(9) mm (to ~1/3 inch) long with 2 to 5 florets; the uppermost floret may be sterile.
At the base of a spikelet is a pair of bracts (glumes) that are both narrowly to broadly lance to egg-shaped, tapering to a pointed tip, awnless, hairless, light green with transparent whitish edging, 3-veined, keeled, the lower glume 2 to 3.8 mm long, the upper glume as long as or slightly larger than the lower glume and shorter than to about as long as the lowest floret. Surrounding a floret is a pair of bracts (lemma and palea), the lemma 2.5 to 4 mm long, egg-shaped with whitish edging, rounded to pointed at the tip, often purple-bronzey near the tip, 5-veined, the lateral veins not reaching the tip of the lemma, long white hairs on the keel and the 2 edge veins, the intermediate vein between the midvein and edge vein obscure and sometimes sparsely hairy, the surface between veins hairless or minutely hairy at least towards the base; the palea is nearly as long as the lemma but narrower, 2-veined, rough or hairy along the veins. The thickened base of the floret (callus) usually has some crinkled hairs though these are sometimes absent; the stalk between florets (rachilla) is up to 1.2 mm long and usually covered in short, straight hairs.
Leaves and stems:
Leaves are mostly basal with 2 or 3 leaves in the lower half of the stem. Leaves are blue-green, flat, erect to spreading, up to 4 inches (10 cm) long, 1 to 3 mm wide, hairless, boat-shaped at the tip, not much reduced in size as they ascend the stem. The uppermost leaf (flag leaf) is at or below the middle of the stem and is shorter than the associated sheath.
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 1 to 4 mm long and lacks a fringe of hairs. Nodes are smooth and usually hidden in the sheaths, sometimes one is exposed, the uppermost node usually positioned on the lower 1/3 of the stem. Stems are blue-green, unbranched, mostly erect, multiple from the base forming clumps, and lack rhizomes or stolons.
Glaucous Bluegrass is a cool-season grass of boreal forest and alpine areas of North America with a few populations in both Russia and Patagonia. In Minnesota, it is almost exclusively found on moss-covered ledges and crevices of cliffs, talus slopes, rocky banks, rock outcrops, and the rocky north shore of Lake Superior. A pair of records from Kittson County in 1958 recorded it in sandy prairies, but the habitat seems a little suspect so the IDs are questionable.
Glaucous Bluegrass is somewhat variable, but is generally recognized by its clump-forming growth, blue-green coloring, nodes usually all hidden in the sheaths, uppermost node on the lower 1/3 of the stem, stem leaves all near the same size, the uppermost leaf at or below the middle of the stem and shorter than its sheath, ligule usually over 1 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, sometimes hairy on intermediate veins, sometimes minutely hairy between veins near the base, usually some crinkled hairs on the callus, and hairy rachillas up to 1.2 mm long (strong magnification required to see).
Poa glauca closely resembles two other Bluegrasses, one native and one introduced from Europe, and all three may be found in similar habitats: Poa interior (Inland Bluegrass) and Poa nemoralis (Wood Bluegrass), both of which have mostly exposed nodes, the uppermost node in the upper 2/3 of the stem, where P. glauca nodes are usually hidden on the lower third of the stem. There are 2 or 3 subspecies (or vars), though these are not universally recognized; subsp. glauca is most common, present in Minnesota and is described above; subsp. rupicola has a hairless callus, lemmas are consistently hairy between the veins, and its range is limited to alpine regions of western North America; subsp. pekulnejensis is only known from Alaska and parts of eastern Russia and forms bulblets on its spikelets.
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- Glaucous Bluegrass in early July
- panicles emerging in mid June
- mature plants in August
- close-up of branches
- hairs are sometimes on intermediate veins and/or between veins near the base
Photos by K. Chayka and Peter M. Dziuk taken in Cook County.
Have you seen this plant in Minnesota, or have any other comments about it?