Poa paludigena (Bog Bluegrass)

Plant Info
Also known as:
Family:Poaceae (Grass)
Life cycle:perennial
  • State Threatened
Habitat:part shade, shade; wet; swamps, bogs, seeps, fens, wet forests, wet meadows
Fruiting season:July
Plant height:4 to 20 inches
Wetland Indicator Status:GP: none MW: OBL NCNE: OBL
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] Open panicle 2 to 4 inches (5 to 10 cm) long, usually erect and pyramidal in outline, the branches usually spreading, with 1 or 2 branches per node and 1 to a few spikelets (flower clusters) along the tip half of a branch. Spikelets are light green at flowering time, flattened, lance-elliptic in outline, 3.2 to 5.2 mm (less than ¼ inch) long with 2 to 5 florets; the uppermost floret may be sterile.

[close-up of spikelet] At the base of a spikelet is a pair of bracts (glumes) that are both shorter than the spikelet, pointed at the tip, awnless, hairless, keeled, rough along the keel, the upper glume 3-veined, the lower glume somewhat smaller and 1-veined. Surrounding a floret is a pair of bracts (lemma and palea), the lemma 2.5 to 4 mm long, blunt to pointed at the tip, keeled, 5-veined, with long white hairs along the lower half to ~¾ of the keel and the lateral veins, surface between the veins hairless; the palea is nearly as long as the lemma, 2-veined, rough along the veins. The thickened base of the floret (callus) has a small tuft of long, crinkly hairs; the stalk between florets (rachilla) is hairless.

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

[photo of stem, ligule and node] Leaves are few, typically 2 to 4 alternate leaves widely spaced along the stem. Leaves are up to 4 inches (10 cm) long, .5 to 2 mm (less than 1/8 inch) wide, hairless, flat, boat-shaped at the tip. The sheath is hairless, smooth to slightly rough, the edges fused for ¼ to 3/5 their length (closed sheath). The ligule (membrane where the leaf blade joins the sheath) is .5 to 2 mm long and lacks a fringe of hairs. Nodes are smooth. Stems are unbranched, weak, ascending to sprawling, smooth to slightly rough, single or a few from the base forming loose clumps, and lack rhizomes or stolons.

Fruit: Fruit type: seed without plume

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


Bog Bluegrass is a native, cool-season grass typically found in wet, shady places such as swamps, bogs and forested seeps. It is rare throughout its range, including Minnesota, where it reaches the northwestern tip of its range. According to the DNR, it was unknown in Minnesota until 1980, when it was found during a biological survey in Pine County. Subsequent surveys discovered a number of other locations, mostly in our east-central counties, but populations are small and restricted to vulnerable wetland habitats. Originally listed as a State Endangered species in 1984, it was reclassified as Threatened in 1996.

Poa species are recognized by their (usually) closed sheaths, leaves with boat-shaped tips, and often long, cobwebby hairs around the base of the floret (callus). Bog Bluegrass is distinguished by its weak stems; flat leaves not more than 2 mm wide and 4 inches long; ligule less than 2 mm long; sheaths closed for ¼ to 3/5 their length; open panicle, only 1 or 2 branches per node, a few spikelets along the tip half of a branch; 2 to 5 florets per spikelet; florets 2.5 to 4 mm long, hairy along the lemma keel, lateral veins, and callus, hairless on the surfaces.

There are some similarities with other Poa species, such as the number and width of leaves, how much of the sheath is closed, arrangement of spikelets on a branch, number of florets in a spikelet, hairs on the lemma veins, and the crinkly hairs around the callus, but in different combinations. Poa paludigena panicles having only 1 or 2 branches per node and lemmas having hairs on lateral veins and the keel but not the surface is a unique combination. It is also a fairly short plant, spindly and inconspicuous, often hiding under other vegetation, sometimes growing on mossy logs.

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More photos

Photos by K. Chayka taken in Aitkin County.


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