E-Flora BC: Electronic Atlas of the Flora of British Columbia

Poa infirma Kunth
diploid annual bluegrass (weak bluegrass)
Poaceae (Grass family)

Introduction to Vascular Plants
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Distribution of Poa infirma
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Species Information

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Annual tufted grass from fibrous roots; stems 2-15 cm tall.
Sheath margins open about 2/3 their length; sterile shoots emerging inside the sheaths with indistinct two-keeled buds protecting the scales; blades 1-4 mm wide, flat, thin; ligules 0.5-3 mm long, the backs smooth, hairless.
Inflorescence an erect panicle, 1-6 cm long, 1.5-3 times longer than wide, the branches 1 to 2 (5) per node, ascending; spikelets laterally compressed, 3-5 mm long, 2- to 6-flowered; the lower glumes 1-nerved; rachillas smooth, hairless, visible from the side, terminal internodes 1/2-3/4 the length of the terminal lemmas; lemmas lanceolate, 2-2.5 mm long, the tips rounded to sharp-pointed, surface smooth, keel, marginal, and lateral nerves short silky-hairy, lateral nerves moderately prominent; calluses hairless; palea keels silky-hairy; flowers bisexual, or the upper ones in a spikelet female; anthers 0.1-0.5 mm long, more or less globe-shaped prior to opening.

Source: The Illustrated Flora of British Columbia

Habitat / Range

Mesic sites in the lowland zone; rare in SW BC, known only from Trial Island; introduced from S Europe.

Source: The Illustrated Flora of British Columbia


Ecological Framework for Poa infirma

The table below shows the species-specific information calculated from
original data (BEC database) provided by the BC Ministry of Forests and Range.
(Updated August, 2013)

Site Information
Value / Class




Elevation (metres) 765 1481 1840
Slope Gradient (%) 5 23 55
Aspect (degrees)
[0 - N; 90 - E; 180 - S; 270 - W]
136 333 330
Soil Moisture Regime (SMR)
[0 - very xeric; 4 - mesic;
8 - hydric]
2 3 6
Modal Nutrient Regime
Number of field plots
 species was recorded in:
Modal BEC Zone Class
All BEC Zones (# of stations/zone) species was recorded in: ESSF(2), IDF(1)


The climate type for this species, as reported in the: "British Columbia plant species codes and selected attributes. Version 6 Database" (Meidinger et al. 2008), is not evaluated, unknown or variable.

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