COMMON NAME

Canada blue-grass


FULL SCIENTIFIC NAME

Poa compressa L.


FAMILY NAME COMMON

Grass family


FAMILY SCIENTIFIC NAME

Poa compressa


IMAGES


Habit

Cross-section of Compressed Stems

Inflorescences

Inflorescence Close-up

Habitat

Roots

NOMENCLATURE/SYNONYMS

Synonyms: None


DESCRIPTION

Botanical Glossary

Poa compressa is a slender, erect, perennial grass that grows 10-70 cm in height (3.9-27.6 in.). It has a creeping root system with long, slender rhizomes that can form an open sod. The culms (stems) of Poa compressa are strongly flattened and cannot easily be rolled between one's fingers and thumb. The bluish-green leaves are 2-4 mm wide (0.08 to 0.16 in.) and can grow up to 10 cm in length (3.9 in.). The tips of the leaves are boat-shaped. The ligules are short, 1-2 mm in length ( 0.04-0.08 in.) and membranous. The inflorescence is a compact, narrow panicle that grows 2-8 cm (0.8-3.9 in.) in length. The inflorescences are green to purplish in color and stand erect. The branches of the panicles often grow in pairs. They have densely clustered spikelets that are 4-6 mm (0.16-0.24 in.) in length and have 3-6 flowers each. The spiklets are borne on very short pedicels, or sometimes have no pedicels at all. The glumes are 1.7-2.6 mm (0.07 -0.10 in.) long, with the first one slightly shorter than the second. The lemma are 2.0-2.8 mm (0.08-0.11 in.) long, firm, sometimes cobwebby at the base and have faint veins. Page References Bailey 152, Fernald 117, Gleason & Cronquist 754, Holmgren 701, Magee & Ahles 158. See reference section below for full citations.


SIMILAR SPECIES

Poa pratensis L. (Kentucky bluegrass) Poa compressa can be distinguished from P. pratensis and other Poa spp. by its flattened stem and its blue-green color. Also, the rhizomes of P. compressa originate below ground and turn downward, but those of P. pratensis start from above ground before turning downward.


REPRODUCTIVE/DISPERSAL MECHANISMS

Poa compressa reproduces by both seeds and rhizomes. It produces numerous, tiny seeds that are primarily dispersed by wind and also by animals. The rhizomes allow it to spread locally, whereas the seeds account for most of its dispersal over distances.


DISTRIBUTION

Poa compressa is native to Europe. It is widely spread throughout North America, where its range extends from Newfoundland to Alaska and south to include all the continental United States with the exception of Florida. Poa compressa is less abundant in the southern parts of this range. It is present in all of the states of New England.


HISTORY OF INTRODUCTION IN NEW ENGLAND

Poa compressa was most likely introduced to North America as a forage plant. The exact timing of its introduction is unclear. There may well have been multiple introductions, some of them accidental. It is clear that Poa compressa was already widespread in the United States by the end of the 19th century. Gray's Manual of Botany, 7th ed. (Robinson, 1908) reports its range as "Newfoundland to South Carolina and westward". Bailey's Manual of Cultivated Plants (1949) describes it as "Extensively naturalized, and used as a pasture-grass; it becomes a persistent weed in tilled hard lands."


HABITATS IN NEW ENGLAND

Abandoned Field,Abandoned Gravel Pit,Agricultural Field,Edge,Open Disturbed Area,Pasture,Roadside,Vacant Lot,Yard or Garden

Poa compressa is primarily a colonizer of disturbed sites. Its seeds require direct light for germination. It is not highly competitive in moist habitats with fertile soils. Instead, it grows well in dry sites or sites with acidic soils, including rocky outcrops and exposed mountain tops. Poa compressa is more problematic in dry areas of the western U.S. and Canada.


THREATS

Poa compressa does not currently pose a big threat to undisturbed natural areas in New England. However, its ability to spread rhizomatously combined with its effective seed dispersal does give it the potential to be a nuisance species in areas that are recovering from disturbance. When it does grow in dense clumps, it has the potential to crowd out native species.


MANAGEMENT LINKS


DOCUMENTATION NEEDS

Documentation required: Herbarium specimen or mounted snippet of the branch with flowers or fruits.
Best time for documentation: Summer, fall.


ADDITIONAL INFORMATION

Integrated Taxonomic Information System
Taxonomic information

USDA Forest Service Fire Effects Information System
Comprehensive information, focus on rangeland and fire ecology

The PLANTS Database
General information and map


REFERENCES

Bailey, L.H.  1949.  Manual of Cultivated Plants.  Macmillan, New York.

Britton, N.L. and A. Brown.  1970.  An Illustrated Flora of the Northeastern United States vol. 2.  Dover Publications Inc., New York. 

Burg, W.J. van der, G. Vierbergen, K.T. Koenders. 1979. Differentiation of Poa species. Seed Sci. Tech. 7:523- 524.

Curtis, J.T. and M.L. Partch. 1948. Effects of fire on the competition between blue grass and certain prairie plants. American Midland Naturalist. 39(2): 437-443.

Fernald, M.L. 1950. Gray's Manual of Botany 8th ed. American Book Co., Boston.

Gleason, H.A. and A.C. Cronquist.  1991.  Manual of Vascular Plants of the Northeastern United States and Adjacent Canada. 2nd ed.  New York Botanical Garden, Bronx, New York.

Hadley, E.B. and B.J. Kieckhefer. 1963. Productivity of two prairie grasses in relation to fire frequency. Ecology 44:389-395.

Holm, L.G., J.V. Pancho, J.P. Herberger and D.L. Plucknett 1979. A Geographical Atlas of World Weeds. John Wiley and Sons, New York, USA.

Holmgren, N.H. 1998. Illustrated Companion to Gleason and Cronquist's Manual.  New York Botanical Garden, Bronx, New York.

Magee, D.W. and H.E. Ahles. 1999.  Flora of the Northeast. University of Massachusetts Press, Amherst.

Morgan, W.E. and J.M. Watkins. 1939. The growth of Kentucky bluegrass and of Canada bluegrass in late spring and in autumn as affected by the length of day. J. Amer. Soc. Agron. 31:767-774.

Sprague, V.G. 1940. Germination of freshly harvested seeds of several Poa species and of Dactylis glomerata. J. Amer. Soc. Agron. 32:715-725.

Stroud, D.J., G.B. Johnson, A.T. Perkins. 1977. The effects of application timing on the control of Canadian bluegrass (Poa compressa) using tebuthiuron, a soil residual herbicide. pp 127. Proc. Northern central weed control conference V. 32.

Swan, F.R., Jr. 1970. Post-fire response of four plant communities in south-central New York state. Ecology. 51(6): 1074-1082.

Tyser, R.W. and C.A. Worley. 1992. Alien flora in grasslands adjacent to road and trail corridors in Glacier National Park, Montana (USA). Conserv. Bio. 6:253-262.  

USDA, NRCS.  2001.  The PLANTS Database, Version 3.1. (http://plants.usda.gov).  National Plant Data Center, Baton Rouge, LA 70874-4490 USA.