Poa saltuensis (Old-pasture Bluegrass)

Plant Info
Also known as: Weak Bluegrass, Drooping Bluegrass, Woodland Bluegrass, Weak Speargrass
Genus:Poa
Family:Poaceae (Grass)
Life cycle:perennial
Origin:native
Habitat:part shade, shade; dry to moist soil; forests, clearings, trail edges, ravines, rocky banks and shores, swamps
Fruiting season:June - August
Plant height:1 to 3 feet
Wetland Indicator Status:none
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] Loose panicle 2 to 8+ inches long, usually nodding, with 1 to 3 (usually 2) ascending to drooping branches at each node. Spikelets (flower clusters) are concentrated towards branch tips, short-stalked, green to yellowish to purple-tinged, flattened, 3 to 5.6 mm (to ~¼ inch) long with 2 to 5 florets, commonly 2 or 3; the uppermost floret may be sterile.

[close-up of spikelets] At the base of a spikelet is a pair of bracts (glumes) that are both pointed at the tip, awnless, hairless, light green to purplish with transparent whitish edging, keeled, 1.7 to 3 mm long, the lower glume 1-veined, the upper glume somewhat larger than the lower glume and 3-veined. Surrounding a floret is a pair of bracts (lemma and palea), the lemma 2.4 to 4 mm long, usually longer than the upper glume, lance-shaped with transparent whitish edging, blunt to sharply pointed at the tip, 5-veined, hairless on the veins and between them; the palea is about as long as or somewhat shorter than the lemma and 2-veined. The thickened base of the floret (callus) has a few long, crinkled hairs.

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

[photo of stem leaves] Leaves are alternate with a few leaves widely spaced along most of the stem. Leaves are flat, thin and not stiff, up to 6 inches long, 2 to 5 mm wide, hairless, boat-shaped at the tip.

[photo of sheath, ligule and node] The sheath is hairless and the edges are fused for 1/3 to 2/3 their length (closed sheath). The ligule (membrane where the leaf blade joins the sheath) is 1 to 4+ mm long, straight to convex across the top edge, though may be jagged, and lacks a fringe of hairs. Nodes are smooth. Stems are unbranched, erect to ascending, a few from the base forming loose clumps, and lack rhizomes or stolons.

Fruit: Fruit type: seed without plume

[photo of maturing 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 2 mm long.

Notes:

Old-pasture Bluegrass is a cool-season grass primarily found in the northeastern quadrant of the state, where it reaches the western edge of its range. Habitats are primarily in the dense to light shade of deciduous, conifer or mixed forests, dry to wet. Poa grasses are most easily recognized by their closed sheathes, leaves with boat-shaped tips, multi-flowered spikelets, and florets usually with long, crinkled hairs on the callus. Old-pasture Bluegrass is one of the few with completely hairless florets except for the callus. It is further recognized by its loose, usually nodding panicle with 1 to 3 branches per node and relatively few spikelets per branch, all concentrated near branch tips.

There are two subspecies, both of which have been recorded in Minnesota, though some references treat them as separate species and others lump them into a single, variable species: subsp. languida (Poa languida) has uppermost ligules 2.6 to 4+ mm long, lemmas with blunt tips that may or may not be thin and translucent for up to .25 mm, anthers mostly less than 1 mm long; subsp. saltuensis has uppermost ligules less than 2.6 mm long, lemmas with pointed or long tapering tips that are thin and translucent for .25 to .5 mm, anthers mostly 1 to 1.5 mm long.

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More photos

Photos by Peter M. Dziuk taken in Cook County.

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