Poa pratensis - L.
Kentucky Bluegrass
Other Common Names: Kentucky bluegrass
Taxonomic Status: Accepted
Related ITIS Name(s): Poa pratensis L. (TSN 41088)
Unique Identifier: ELEMENT_GLOBAL.2.149735
Element Code: PMPOA4Z210
Informal Taxonomy: Plants, Vascular - Flowering Plants - Grass Family
Kingdom Phylum Class Order Family Genus
Plantae Anthophyta Monocotyledoneae Cyperales Poaceae Poa
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Concept Reference
Concept Reference: Kartesz, J.T. 1999. A synonymized checklist and atlas with biological attributes for the vascular flora of the United States, Canada, and Greenland. First edition. In: Kartesz, J.T., and C.A. Meacham. Synthesis of the North American Flora, Version 1.0. North Carolina Botanical Garden, Chapel Hill, N.C.
Concept Reference Code: B99KAR01HQUS
Name Used in Concept Reference: Poa pratensis
Taxonomic Comments: When broadly treated as by Kartesz (1999), includes plants native in North America as well as plants introduced to North America from Eurasia ("Kentucky Bluegrass"). If narrowly treated as in Kartesz (1994), Poa pratensis is primarily if not exclusively Eurasian, widely cultivated worldwide and often persisting or escaping, although considered by some to be native in the more northern portions of North America.
Conservation Status

NatureServe Status

Global Status: G5
Global Status Last Reviewed: 16May2016
Global Status Last Changed: 26Feb2001
Ranking Methodology Used: Ranked by inspection
Rounded Global Status: G5 - Secure
Nation: United States
National Status: NNR
Nation: Canada
National Status: N5 (08Mar2016)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Alabama (SNR), Alaska (SNR), Arizona (SNR), Arkansas (SNR), California (SNR), Colorado (SNA), Connecticut (SNR), Delaware (SNA), District of Columbia (SNA), Florida (SNR), Georgia (SNR), Hawaii (SNA), Idaho (SNR), Illinois (SNA), Indiana (SNR), Iowa (SNA), Kansas (SNR), Kentucky (SNA), Louisiana (SNR), Maine (SNR), Maryland (SNR), Massachusetts (SNR), Michigan (SNA), Minnesota (SNA), Mississippi (SNR), Missouri (SNR), Montana (SNA), Nebraska (SNR), Nevada (SNR), New Hampshire (SNR), New Jersey (SNR), New Mexico (SNR), New York (SNR), North Carolina (SNA), North Dakota (SNR), Ohio (SNR), Oklahoma (SNR), Oregon (SNR), Pennsylvania (SNA), Rhode Island (SNR), South Carolina (SNR), South Dakota (SNR), Tennessee (SNR), Texas (SNR), Utah (SNR), Vermont (SU), Virginia (SNA), Washington (SNR), West Virginia (S4), Wisconsin (SNR), Wyoming (SNA)
Canada Alberta (S5), British Columbia (SNR), Labrador (S3S4), Manitoba (S5), New Brunswick (S5), Newfoundland Island (S3), Northwest Territories (S5), Nova Scotia (S5), Nunavut (S4), Ontario (S5), Prince Edward Island (S5), Quebec (S5), Saskatchewan (SNA), Yukon Territory (S5)

Other Statuses

NatureServe Global Conservation Status Factors

Other NatureServe Conservation Status Information

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
NOTE: The distribution shown may be incomplete, particularly for some rapidly spreading exotic species.

U.S. & Canada State/Province Distribution
United States AK, AL, AR, AZ, CA, COexotic, CT, DCexotic, DEexotic, FL, GA, HIexotic, IAexotic, ID, ILexotic, IN, KS, KYexotic, LA, MA, MD, ME, MIexotic, MNexotic, MO, MS, MTexotic, NCexotic, NDexotic, NE, NH, NJ, NM, NV, NY, OH, OK, OR, PAexotic, RI, SC, SD, TN, TX, UT, VAexotic, VTnative and exotic, WA, WI, WV, WYexotic
Canada AB, BC, LB, MBnative and exotic, NB, NF, NS, NT, NU, ONnative and exotic, PE, QC, SKexotic, YT

Range Map
No map available.

U.S. Distribution by County Help
State County Name (FIPS Code)
NH Coos (33007)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
01 Lower Androscoggin (01040002)+*, Saco (01060002)+, Waits (01080103)+*
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
General Description: Poa pratensis is a shallowly rooted, rhizomatous perennial grass.
Technical Description: Poa pratensis is distinguished by its caespitose, terete to flattened, glabrous culms 30 to 100 cm tall (Hitchcock 1950, Great Plains Flora Assoc. 1986); rounded or flattened sheathes with ligules 1-5 mm in length (Fernald 1950); and flat to folded leaf blades 9 to 6 mm wide, up to 37 cm long, with boat-shaped tips (Fernald 1950, Great Plains Flora Assoc. 1986). The ovoid inflorescence is composed of crossed spikelets with 3-5 flowers (Hitchcock 1950, Gleason and Cronquist 1953) the veins of the pubescent, keeled lemmas are sharp (Mohlenbrock 1975, Hitchcock 1950, Van der Berg et al. 1979). The teeth of the palea are coarse, remote and not extending to the apex (Van der Berg et al. 1979).
Diagnostic Characteristics: The genus Poa is distinguished by its flat leaf blades, 2-6 flowered panicles, 1-3 nerved glumes and tuft of cobwebby hairs at the base of the 5-nerved lemmas (Gleason 1957, Mohlenbrock 1972, Hitchcock 1950).
Reproduction Comments: On any given parent plant the number of axillary buds is dependent on the number of leaves. Etter (1951) reports that in dry, shady localities, Kentucky bluegrass may develop as few as 7 to 9 leaves, 12 to 14 in a meadow, and as many as 18 in a moist pasture. Each axillary bud has the developmental possibility of early tiller formation or delayed rhizome development.

In rangeland terminology a "tiller" often refers to any aerial shoot. In the strict parlance of developmental morphology a "tiller" is an aerial shoot that develops in the axillary bud of live leaf tissue (Etter 1951, Dahl and Hyder 1977). These new shoots develop root systems of their own and are hence a method of vegetative reproduction. Because of their origin, tillers always develop in close proximity to the parent plant. Young tillers derive their nutrition from the parent plant until they have attained full growth (Dahl and Hyder 1977). Although tillers develop true root systems of their own, these systems are not extensive (Etter 1951) and mature tillers neither translocate nor receive carbohydrates to and from other shoots derived from the same parent plant. There is a high mortality of tillers during the season of formation (Etter 1951).

Tillering is favored by cool temperatures (Etter 1951, Darrow 1939) and short day lengths (Evans and Watkins 1939, Evans 1927) and reaches its maximum in spring and fall, but declines in midsummer. Tillering is induced by early removal of developing flowering culms while the floral initiates are still enclosed within the sheath (booth stage) (Dahl and Hyder 1977). Etter (1951) reports that tillering is correlated with short leaves and, in a separate context, that Poa pratensis is more likely to develop long leaves in the shade. Well-lit situations that foster an abundance of shorter leaves may therefore enhance tillering. Etter (1951) reports that tillering is encouraged by April mowing to prevent flowering, fall grazing, fall nitrogen fertilization, fall irrigation and removal of dead plant material and shading.

Both Poa pratensis and Poa compressa are rhizomatous perennial grasses. Some North American fields of Poa pratensis are known to be as old as 60 years (USDA 1948). Volland (1978) attributes the inter-seasonal longevity of bluegrass to the activity of the rhizomes.

Axillary buds that have not formed tillers can develop into rhizomes, lateral shoots that penetrate the enveloping leaf sheath and develop underground (Dahl and Hyder 1977, Etter 1951). Rhizomes can form on the surface of the soil (Evans and Ely 1935, Etter 1951), but soon turn downward. Rhizomes account for bluegrass's sod-forming capability and can extend the horizontal growth of the plant as much as 2 square meters in 2 years (Kannenberg and Wrede 1934). The mode of elongation is the same as for aboveground shoots. The length of the rhizome is a function of the degree of internode elongation. Under conditions of drought or on excessively drained soils, short internodes (and hence short rhizomes) are produced. Short sprout-like rhizomes appear to increase under adverse conditions such as high temperatures (Harrison 1934) fire injury, or too close grazing and mowing (Etter 1951).

Rhizome formation and growth occurs throughout the year except late winter and early spring. Initiation of new rhizomes from axillary buds that have remained dormant overwinter invariably occurs when the inflorescence begins to elongate (Etter 1951). Brown (1939) found that rhizome elongation peaks between 60 and 70 degrees F. Evans and Ely (1935) report a midsummer peak of rhizome formation in Ohio. Summer- formed rhizomes can remain dormant until the following spring or develop into aerial shoots anytime during the growing season.

Rhizomes constitute a major sink for storage of carbohydrates in Poa pratensis. Brown (1943) reports that late autumn is the most favorable period for carbohydrate storage in Kentucky bluegrass.

Palustrine Habitat(s): SCRUB-SHRUB WETLAND
Terrestrial Habitat(s): Grassland/herbaceous, Old field
Habitat Comments: There is some disagreement whether Poa pratensis is native in the northern tier of states and Canada (Fernald 1950, Great Plains Flora Assoc 1986, Gleason and Cronquist 1953) or native in Eurasia and introduced throughout its North American range (Hitchcock 1950, Mohlenbrock 1972, USDA 1948). Kentucky bluegrass is planted in some areas for forage and is widely used for turf.

Kentucky bluegrass is favored by moist conditions, including reservoir shores (Hoffman et al. 1980). It can withstand flooding (Schalitz 1977) flooding with subsequent freezing, ice and snow (Beard 1964). The interaction of the effects of soil texture and climate on Poa pratensis is demonstrated by its high frequency on drier sites of Ontario old fields on shallow circumneutral soils overlying gravel (Maycock and Guzikowa 1983), low frequency on sandy soils in Wisconsin (Kline pers. comm.), and absence from sandy soils in Nebraska (Steuter pers. comm.).

Economic Attributes
Economic Uses: FORAGE/BROWSE
Management Summary Not yet assessed
Population/Occurrence Delineation Not yet assessed
Population/Occurrence Viability
U.S. Invasive Species Impact Rank (I-Rank)
Disclaimer: While I-Rank information is available over NatureServe Explorer, NatureServe is not actively developing or maintaining these data. Species with I-RANKs do not represent a random sample of species exotic in the United States; available assessments may be biased toward those species with higher-than-average impact.

I-Rank: Medium
Rounded I-Rank: Medium
I-Rank Reasons Summary: Poa pratensis is an invasive that spreads aggressively and readily outcompetes native vegetation, especially in prairie habitats.
Subrank I - Ecological Impact: Medium
Subrank II - Current Distribution/Abundance: High
Subrank III - Trend in Distribution/Abundance: Medium/Low
Subrank IV - Management Difficulty: Medium/Low
I-Rank Review Date: 07Dec2005
Evaluator: Maybury, K.
Native anywhere in the U.S?
Native Range: Eurasia. Many sources treat the species as wholly non-native in the U.S.. Possibly only of native origin in the northern U.S. and Canada and introduced elsewhere (Fernald 1950, Gleason and Cronquist 1953).

Download "An Invasive Species Assessment Protocol: Evaluating Non-Native Plants for their Impact on Biodiversity". (PDF, 1.03MB)
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Screening Questions

S-1. Established outside cultivation as a non-native? YES

S-2. Present in conservation areas or other native species habitat? Yes

Subrank I - Ecological Impact: Medium

1. Impact on Ecosystem Processes and System-wide Parameters:Low significance
Comments: Some minor impacts assumed since this species can form dense sods and retard or cause long-term alterations in successional patterns (Butterfield et al. 1996). May also increase soil water content in sod (Glenn and Welker 1996 as cited in Lapina and Carlson, not dated).

2. Impact on Ecological Community Structure:Low significance
Comments: Forms dense mats and is capable of changing the density of the herbaceous layer (Uchytil 1993).

3. Impact on Ecological Community Composition:High significance
Comments: In natural areas, P. pratensis is highly competitive with native species, reducing species diversity and altering floristic composition (Slather 1996).

4. Impact on Individual Native Plant or Animal Species:Medium/Low significance
Comments: A host for certain insects and diseases (Butterfield et al. 1996) and a food source (replacing native food sources?) for elk, mule deer, bighorn sheep, small mammals and birds (Uchytil 1993). Slather (1996) notes that it is less nutritious than native mixed-grass prairie speices for cattle, so it may have some negative impact on wildlife as well. In addition, may hybridize with native bluegrass populations (Uchytil 1993).

5. Conservation Significance of the Communities and Native Species Threatened:High significance
Comments: P. pratensis was found to be the most frequently occurring and the most abundant (based on % cover) exotic species in tallgrass prairie remnants (Cully et al. 2003). At Sequoia, Kings Canyon and Yosemite national parks, it was categorized as an exotic plant having great impact on native vegetation and that was very broadly distributed in the parks (Moore and Gerlach 2001). The parks include a diverse array of high quality vegetaton types including chaparral, oak woodlands, conifer forests, meadows, and alpine plant communities (Moore and Gerlach 2001). Uchytil (1993) notes that it can dominate the understory several western habitats, including aspen stands and riparian areas.

Subrank II. Current Distribution and Abundance: High

6. Current Range Size in Nation:High significance
Comments: Assuming most material is non-native, this species has naturalized in all 50 states.

7. Proportion of Current Range Where the Species is Negatively Impacting Biodiversity:High/Moderate significance
Comments: Some sources emphasize the negative impacts on the prairie region, but other areas are clearly impacted as well (e.g., see Uchytil 1993, Moore and Gerlach 2001; Lapina and Carlson, not dated).

8. Proportion of Nation's Biogeographic Units Invaded:High significance

9. Diversity of Habitats or Ecological Systems Invaded in Nation:High significance
Comments: Tallgrass and mixedgrass prairies, meadows, open woodlands (aspen, ponderosa pine, etc.), sagebrush, western riparian communities, etc. (e.g., Wennerberg 2004).

Subrank III. Trend in Distribution and Abundance: Medium/Low

10. Current Trend in Total Range within Nation:Low significance
Comments: This species is already occuring throughout the generalized range and is assumed to be stable.

11. Proportion of Potential Range Currently Occupied:Insignificant
Comments: Assumed to have occupied most of its potential range.

12. Long-distance Dispersal Potential within Nation:High significance
Comments: This is one of the most commonly sold and planted turfgrasses for lawns and other grassy areas. Also planted for forage (favored because it allows early spring pasturing) and mixed into seed mixes used for revegetation of roadbanks (Wennerberg 2004). Over 100 cultivars have been developed (Lapina and Carlson, not dated).

13. Local Range Expansion or Change in Abundance:Medium/Low significance
Comments: Almost certainly expanding at at least a moderate rate locally. Thought to be increasing its range in Sequoia, Kings Canyon and Yosemite national parks (Moore and Gerlach 2001). Increases with grazing (Slather 1996). Disturbance, in general, will lead to increases as the species can become established on disturbed sites faster than many other plant species (Wennerberg 2004).

14. Inherent Ability to Invade Conservation Areas and Other Native Species Habitats:Moderate significance
Comments: Spreads readily via seed into areas with light and open (disturbed) soil, but the seeds probably do not germinate and establish plants in intact vegetation often. However, the species does spread into established prairies via rhizomes that "penetrate between the other plants" (Slather 1996). Rhizomes can extend the horizontal growth of the plant by as much as 2 square meters in 2 years (Kannenberg and Wrede 1934 cited in Slather 1996).

15. Similar Habitats Invaded Elsewhere:Unknown

16. Reproductive Characteristics:Moderate significance
Comments: Spreads by seeds and rhizomes and produces large numbers of seeds (Slather 1996). Over 1,000 seeds per plant have been documented and over 800,000 seeds per square meter (Lapina nad Carlson, not dated).

Subrank IV. General Management Difficulty: Medium/Low

17. General Management Difficulty:Medium/Low significance
Comments: Can be maintained by repeated fire in most systems (see Slather 1996).

18. Minimum Time Commitment:High/Low significance
Comments: Seeds can germinate within 4 years after burial (Slather 1996). In Kansas and Nebraska 3 sucessive years of spring burning will convert to dominance by native warm season grasses, but farther north much longer periods of annual burning may be required (Slather 1996). Managment that aims to maintain other cool season native species while still reducing P. pratensis may be much more challenging (Slather 1996).

19. Impacts of Management on Native Species:Low significance
Comments: Control can be accomplished simultaneously with managing for native species (see Slather 1996), although some managment activities will adversely impact natives.

20. Accessibility of Invaded Areas:High significance
Comments: Widely planted on private lands.

Other Considerations: This I-rank assessment is based on the assumption that most Poa pratensis material in the U.S. is non-native in origin. Kartesz (1999) considers P. pratensis partly native in the U.S., while many other sources consider it non-native. Kartesz (1994, 1999) lumps the Canadian (and western U.S.) native P. alpigena into P. pratensis as P. pratensis ssp. alpigena. Poa pratensis ssp. pratensis is considered introduced into the United States from Europe (Hitchcock 1951), but may be considered native along the northern boundary of the U.S and in Canada (Gleason and Cronquist 1991). Hulten (1968) treats P. pratensis as an introduced weed in Alaska.
Element Ecology & Life History Edition Date: 20Nov1987
Element Ecology & Life History Author(s): N. SATHER, MRO

Botanical data developed by NatureServe and its network of natural heritage programs (see Local Programs), The North Carolina Botanical Garden, and other contributors and cooperators (see Sources).

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