Agrostis gigantea (Redtop)

Plant Info
Also known as: Black Bent Grass
Family:Poaceae (Grass)
Life cycle:perennial
  • Weedy
Habitat:part shade, sun; average to moist disturbed soils; waste areas, roadsides, fields, railroads, along shores
Fruiting season:July - September
Plant height:1 to 4 feet
Wetland Indicator Status:GP: FACW MW: FACW NCNE: FACW
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

Pick an image for a larger view. See the glossary for icon descriptions.

Detailed Information

Flower: Cluster type: panicle

[photo of flowering spikes] Loose panicles, taller than wide, 3 to 10 inches long, egg-shaped to pyramidal in outline, the main branches whorled at the stem nodes and spreading to ascending. Spikelets (flower clusters) are mostly appressed near the tips of the main branches, though at least some branches have spikelets all the way to the branch base. Spikelets are typically purplish red, somewhat flattened, lance-shaped tapering to a pointed tip, with a single floret and a short, straight, rough-textured stalk.

[photo of cluster branches] At the base of a spikelet is a pair of bracts (glumes) that are lance-shaped tapering to a pointed tip, 1-veined, 1.7 to 3.2 mm long, the upper and lower glumes about equal. Surrounding the floret is a pair of bracts (lemma and palea), both oblong-elliptic, papery thin, translucent whitish and usually obscurely veined, the lemmas smaller than the glumes, 1.5 to 2.2 mm long, the palea about half as long as the lemma. Lemmas are usually awnless, occasionally with an awn up to 1.5 mm long. The thickened base of the floret (callus) may have sparse hairs .1 to .5 mm long.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of stem leaves] Leaves are alternate, 2 to 8 inches long, up to 1/3 inch (2 to 8mm) wide, flat, hairless and mostly smooth on both surfaces.

[photo of sheath, ligule and node] Sheaths are mostly smooth, the edges overlapping near the tip or sometimes more widely separated, forming a long “V” at the front. The ligule (membrane where the leaf joins the sheath) is longer than wide, the top edge rounded to straight across and slightly jagged, the upper ligules up to ¼ inch (7 mm) long, the lower ligules shorter. Nodes are smooth and typically reddish. Stems are smooth, multiple from the base forming loose clumps, unbranched, sometimes prostrate at the base and sharply angled up from the lower node (geniculate), erect to ascending above, may root at the lower nodes, and typically forms colonies from long rhizomes.

Fruit: Fruit type: seed without plume

[photo of immature (green) and mature (brown) florets Florets drop away when mature, leaving the glumes behind persisting on the stalk. The grain is elliptic, 1 to 1.5 mm long.


Redtop was introduced as an agricultural crop, escaped cultivation, and is now a common weed of roadsides, farm fields and other disturbed soils. While the distribution map indicates it is absent from several counties in Minnesota, it is likely another under-reported weed and is present statewide. The typically purplish-red panicle with ascending to spreading branches, spikelets with a single floret, the long ligule, and colonies formed by rhizomes (underground stems) are a pretty distinctive combination.

In shadier habitats it is less strongly red in color and can be mistaken for the related Creeping Bentgrass (Agrostis stolonifera), which is a smaller plant, has panicle branches that are only spreading during anthesis and become ascending to appressed after pollination, has narrower leaves, and its colonies are formed by stolons (above ground runners), not rhizomes. Of the 5 Agrostis species known to be in Minnesota, A. gigantea and A. stolonifera both have paleas about half as long as the lemmas, where the others have paleas that are minute at best and more often lack paleas altogether. Magnification is recommended.

Native Plant Nurseries, Restoration and Landscaping Services ↓

Map of native plant resources in the upper midwest

  • ReWild Native Gardens
  • Out Back Nursery
  • Shop for native seeds and plants at!
  • Shooting Star Native Seeds - Native Prairie Grass and Wildflower Seeds
  • Morning Sky Greenery - Native Prairie Plants

More photos

Photos by K. Chayka taken in Ramsey County. Photos courtesy Peter M. Dziuk taken in Anoka, Kittson and Marshall counties.


Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Linda Simmons - South Dakota 8 miles west of border
on: 2020-07-13 12:30:05

I just identified this grass as Agrostis gigantea and see that it is an introduced species. I have a colony of it , almost a monoculture on 4 acres of pasture. I intensively grazed a small paddock 3 yrs ago in the spring and fall to reduce brome and allow warm season plants to increase. Well they sure did but unfortunately the wrong warm season grass "took over". This species does have grazing value but I think I'll try to interseed some native warm season grasses now that I know I have a weed. I'll send a photo soon. Thanks for your work on this website. Linda

Posted by: Linda Simmons - SD 8 miles from border of Big Stone County
on: 2020-07-13 12:55:32

I hope that I have misidentified the plant so I'll get some specimens sent and find a botanist to which to send them.

Post a comment

Note: All comments are moderated before posting to keep the riff-raff out. An email address is required, but will not be posted—it will only be used for information exchange between the 2 of us (if needed) and will never be given to a 3rd party without your express permission.

For info on subjects other than plant identification (gardening, invasive species control, edible plants, etc.), please check the links and invasive species pages for additional resources.


Note: Comments or information about plants outside of Minnesota and neighboring states may not be posted because Id like to keep the focus of this web site centered on Minnesota. Thanks for your understanding.