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

Poa pratensis L.
Kentucky bluegrass
Poaceae (Grass family)

Introduction to Vascular Plants

© Jamie Fenneman  Email the photographer   (Photo ID #4023)

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Distribution of Poa pratensis
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Species Information

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General:
Perennial, densely to loosely tufted grass from fibrous roots and rhizomes or sometimes isolated shoots; stems erect or decumbent, 30-70 (100) cm tall/long, lowermost nodes usually not exserted.
Leaves:
Sheaths hairless or infrequently sparsely to moderately hairy, margins open 1/2-3/4 their length; sterile shoots breaking through sheath bases and emerging inside sheaths; basal bladeless leaves present; blades 0.4-4.5 mm wide, flat or folded, infrequently in-rolled, lax to moderately firm, upper surface sometimes with sparse soft straight hairs; ligules 1-2 (3) mm long, the tips blunt to rounded, the margins slightly rough or smooth towards the tips, the backs smooth or slightly rough.
Flowers:
Inflorescence a panicle, 3-15 (18) cm long, narrowly egg-shaped to narrowly or broadly pyramidal, loosely congested to open, the branches 1 to 7 (9) per node, round, smooth or rough, spikelets usually crowded in terminal 1/2; spikelets laterally compressed, 4-7 mm long, 2- to 5-flowered; glumes distinctly keeled, the keels smooth to moderately rough, the lower glumes usually narrowly lanceolate, 3-nerved, the upper glumes distinctly shorter to nearly equalling the lower lemmas; rachilla internodes mostly less than 1 mm long, smooth, hairless; lemmas lanceolate, 2-4.3 (6) mm long, the tips sharp-pointed, surface membranous, smooth or minutely bumpy, the keels and marginal nerves long silky-hairy (lateral nerves infrequently minutely soft-hairy to short silky-hairy), hairless between the nerves, lateral nerves prominent; calluses copiously cobwebby; palea keels rough, medially some paleas short silky-hairy, hairless between the keels (or rarely sparsely short straight-hairy); flowers bisexual, infrequently bulbiferous; anthers infrequently aborted late in development or 1.2-2 mm long.
Notes:
At least 6 subtly distinct facultatively apomictic subspecies occur in BC. These are extremely difficult to distinguish in North America. A hybrid, P. secunda ssp. juncifolia x P. pratensis (P. x limosa Scribn. & Williams [P. x fibrata Swallen]), is rare in alkaline meadows of SC BC

1. Flowers forming bulbils, panicles more or less linear, native in the subalpine and alpine zones of NW BC............... ssp. colpodea (Th. Fries) Tzvelev

1. Flowers usually not forming bulbils, panicles broader.

2. Plants usually less than 25 cm tall, somewhat covered with a bluish coating; panicle branches arising from lower nodes in groups of 1 or 2 (3); introduced in coastal BC............... ssp. irrigata H. Lindm.

2. Plants 20-100 cm tall, the larger plants without a bluish coating; panicle branches arising from lower nodes in groups of 3 to 5; ranges various.

3. Blades of the vegetative shoots in-rolled, less than 0.7 mm wide, elongated, 10-40 cm long, distinctly narrower than those of the flowering shoots; panicle branches smooth or sparsely rough; sporadically introduced in SW BC.................... ssp. angustifolia (L.) Lej. 3. Blades of the sterile shoots flat or folded and in-rolled on the margins, mostly more than 0.8 mm wide, not differentiated from those of the flowering shoots in form; panicle branches smooth or rough.

4. Panicles 3-6 cm long, contracted at maturity, blades of sterile shoots 3-15 cm long, firm, folded and in-rolled on the margins, often sparsely soft-hairy above (also present in ssp. angustifolia); native of semiarid grasslands and forests in SE BC................ ssp. agassizensis (Boivin & D. Love) Taylor & MacBryde

4. Panicles 4-15 cm long, open at maturity, blades flat or folded, mostly smooth above.

5. Spikelets lanceolate, strongly purple-coloured; lemmas long-hairy on the intermediate nerves or smooth; paleas rough or long-hairy on the lower portion of the keels; panicles narrowly pyramidal, the branches smooth; leaf blades of the vegetative shoots folded; subalpine and alpine plants of N BC............... ssp. alpigena (Lindm.) Hitt.

5. Spikelets broadly lanceolate to egg-shaped, green or somewhat purplish; lemmas smooth, hairless between the keels and marginal nerves; paleas rough on the keels; panicles pyramidal, the branches minutely rough; leaf blades of the vegetative shoots flat or folded; widely introduced in BC....................... ssp. pratensis

Source: The Illustrated Flora of British Columbia

USDA Species Characteristics

Flower Colour:
Yellow
Blooming Period:
Mid Spring
Fruit/Seed characteristics:
Colour: Brown
Present from Spring to Summer
Source:  The USDA

Habitat / Range

Moist to dry meadows, shrublands, open forests and disturbed sites in all vegetation zones; infrequent to common throughout BC; introduced from Eurasia as a lawn and pasture grass (ssp. pratensis, ssp. irrigata and ssp. angustifolia) or native in Canada and the W U.S. (ssp. agassizensis, ssp. alpigena, and ssp. colpodea).

Source: The Illustrated Flora of British Columbia

Ecology

Ecological Framework for Poa pratensis

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

Minimum

Average

Maximum

Elevation (metres) 20 945 2395
Slope Gradient (%) 0 15 230
Aspect (degrees)
[0 - N; 90 - E; 180 - S; 270 - W]
0 195 360
Soil Moisture Regime (SMR)
[0 - very xeric; 4 - mesic;
8 - hydric]
0 3 8
Modal Nutrient Regime
Class
C
Number of field plots
 species was recorded in:
1929
Modal BEC Zone Class
IDF
All BEC Zones (# of stations/zone) species was recorded in: AT(5), BAFA(7), BG(185), BWBS(24), CDF(36), CWH(29), ESSF(106), ICH(41), IDF(898), MH(1), MS(125), PP(193), SBPS(53), SBS(76), SWB(23)

Climate

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.

Synonyms and Alternate Names

Poa agassizensis B. Boivin & D. Löve
Poa angustifolia L.
Poa pratensis subsp. agassizensis (B. Boivin & D. Löve) Roy L. Taylor & MacBryde
Poa pratensis subsp. angustifolia (L.) Lej.
Poa pratensis var. angustifolia (L.) Gaudin
Poa pratensis var. domestica Laest.
Poa pratensis var. gelida (Roem. & Schult.) Böcher
Poa pratensis var. iantha Wahlenb.

Taxonomic and Nomenclatural Links

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General References