Poa compressa
(Canada bluegrass)

Preferred Common Name

• Canada bluegrass

Other Scientific Names

• Paneion compressum (L.) Lunell
• Poa compressa f. depauperata Millsp.
• Poa compressa var. sylvestris Torr.
• Poa langeana Rchb.
• Poa pallens Poir.
• Poa planicularis F.H.Wiggers
• Poa planiculmis Weber
• Poa polynoda Parn.
• Poa subcompressa Parn.
• Poa thurmanniana Montandon

International Common Names

• English: Canadian bluegrass; flattened meadow grass
• Spanish: poa comprimada
• French: pâturin comprimé; pâturin du Canada
• Chinese: jia na da zao shu he
• Portuguese: poa-chata

Local Common Names

• North America: English bluegrass; wire grass
• Canada: creeping Poa; smaller blue grass; Virginia blue grass
• Germany: Rispengras, Flaches; Rispengras, Platthalm-; Rispengras, Zusammengedrücktes
• Italy: gramigna compressa; ruba lana; strappa lana
• Japan: koichigotsunagi
• Korea, Republic of: jompoapul
• Netherlands: beemdgras, plat
• Russian Federation: mjatlik spljusnutyj
• Sweden: groee, berg-
• USA: flat-stem bluegrass

EPPO code

• POACO (Poa compressa)

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Monocotyledonae
•                     Order: Cyperales
•                         Family: Poaceae
•                             Genus: Poa
•                                 Species: Poa compressa

Poa compressa is a member of the family Poaceae. It was one of the many species described in Species Plantarum by Carl Linnaeus in 1753. Poa is Greek for fodder and compressa is Latin for flattened, named for the flattened stems which are only present in this one species in the genus Poa. One of the common names for this species is Canada (or Canadian) bluegrass, reflecting its early introduction to Canada. 

The following description comes from the Flora of China Editorial Committee (2015): Perennials, strongly rhizomatous, shoots extravaginal. Culms wiry, compressed, erect, often geniculate at base, simple or sparsely tufted, 15–50(–60) cm tall, 1.5–2 mm wide, nodes compressed, 3–6, 2–5 exserted. Leaf sheaths compressed to keeled, smooth, uppermost closed for 1/10–1/5 of length; blades flat, 5–12 cm × 1.4–4 mm, surfaces smooth or adaxially scabrid; ligule 1–3 mm, abaxially scabrid, truncate to obtuse. Panicle contracted or slightly open, erect, narrow, 4–11 × 0.5–1(–3) cm; branches erect or steeply ascending, or eventually spreading, 1–3 per node, densely scabrid angled from base, longest 2–4 cm with spikelets moderately crowded from the base or in distal 2/3. Spikelets ovate-lanceolate, 3.5–5 mm, florets 2–4; glumes lanceolate, nearly equal, 2–3 mm, 3-veined, apex acute or thinly mucronate, keel scabrid, rachilla smooth or minutely bumpy; lemmas oblong, 2.3–3.5 mm, apex obtuse, keel shortly villous for 2/3 of length, marginal veins to 1/3, intermediate veins faint, areas between veins glabrous; callus sparsely webbed or glabrous; palea keels scabrid. Anthers 1.3–1.8 mm. Caryopses 1.5 mm long.

P. compressa was introduced into Canada in the late 1700’s (St John et al., 2012) and into much of North America in the early 1800s (Clark and Malte, 1913). It was found along the Saskatchewan River in Canada in 1823 and at other isolated locations unfrequented by European explorers by the early 1800s (Oakley, 1910). It has since spread throughout almost all the continental USA and Canada. The spread in North America is thought to have been as a contaminant of Kentucky bluegrass (P. pratensis) seed (St John et al., 2012). It has been cultivated for pastures in poor soils (Hitchcock, 1951). It was introduced into New Zealand and is now fully naturalized (Edgar, 1986).

Soil drainage

• free
• impeded

Soil reaction

• acid
• neutral

Soil texture

• heavy
• light
• medium

Special soil tolerances

• infertile

P. compressa has been deliberately introduced by man into new countries for use as a forage grass on poor soils, for controlling erosion on disturbed sites, and for low maintenance landscaping. It has also been spread by contamination of P. pratensis seed. Once introduced, it is spread effectively locally by rhizomes, and over longer distances through the numerous tiny seeds, dispersed by both wind and animals (Invasive Plant Atlas of New England, 2015). Cattle and deer can carry P. compressa seeds long distances (Klein, 2008).

P. compressa may become weedy or spread from its intended growing area (for erosion control or landscaping) to adjoining plant communities and displace more desirable vegetation if not properly managed (St John et al., 2012). In Alaska, it is reported to have little impact on native plant communities or successional processes (Klein et al., 2008). In New England, it does not pose a large threat to undisturbed natural areas, but has potential to be a nuisance in areas recovering from disturbance, and could crowd out native species when it grows in dense clumps (Invasive Plant Atlas of New England, 2015). Together with P. pratensis, it can out-compete native species for light and water in British Columbia (Garry Oak Ecosystems Recovery Team, 2015).

In trying to reestablish the Lakeside Daisy (Hymenoxys acaulis var. glabra) at the upland habitats of Lockport and Romeoville Prairies, Illinois, proliferation of herbaceous plants, including P. compressa, has shaded and/or outcompeted the daisy, making control of P. compressa and other introduced plants vital to this endangered species (US Fish and Wildlife Service, 1990).

• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Is a habitat generalist
• Pioneering in disturbed areas
• Tolerant of shade
• Has propagules that can remain viable for more than one year
• Reproduces asexually

• Competition - monopolizing resources
• Competition - shading

• Highly likely to be transported internationally accidentally
• Difficult to identify/detect as a commodity contaminant

Clark and Malte (1913) reported that on poor clay soils, P. compressa grew better than the related pasture grass P. pratensis (Kentucky Blue Grass). Its’ early use was as a permanent pasture grass which thrived under close grazing. More recently, St John et al. (2012) state that the primary use is for controlling erosion on disturbed sites such as roadsides and mined land, heavily used recreational areas, and for low maintenance landscaping. The grass provides food for deer, small mammals and birds, which utilize both the seeds and leaves (St John et al., 2015; Illinois Wild Flowers, 2015; Native Plant Database, 2015).