Redtop is a naturalized perennial grass often used for erosion control as it can form dense tufts. It has a rhizomatous root system, but does not send out stolons.
The stems are usually erect, from 4 to 48 inches high but are sometimes bent at he base such that lower stem nodes can take root.
Leaves are narrow, flat, about 3/8 inch wide and short, up to 4 inches long, sparse on the culm, more clustered at the base. Ligules are longer than wide, with the back side usually rough but sometimes smooth. The Ligule tops are rounded to truncate.
The inflorescence is pyramidal in shape, less than 1/2 the length of the stem, branches spreading, slightly rough, with the spikelets found on the outer half of the branch. The array is reddish in color and can be up to 10 inches long. It matures early. The spikelets are narrowly ovate to lanceolate, green and usually strongly tinged with purple. The glumes are sub-equal, lemmas are 3 to 5 veined but not always conspicuous, usually without awns. Anthers number 3.
Habitat: Redtop is found in much of the Great Plains and it can tolerate wet or dry conditions but is generally found in areas where there is moisture or recent moisture such as after flooding.
Names: The genus Agrostis, is a Greek word for a certain grass. The species, gigantea, means unusually tall or large, referring to the large flowering panicle being almost half the plant height. The author name for the plant classification - ‘Roth’ is for Albrecht Wilhelm Roth (1757-1834) German botanist who published his research and was later associated with the University of Jena Botanical Institute.
Comparisons: A confusing species is A. stolonifera, Spreading Bentgrass, which has a somewhat smaller panicle and the root system forms stolons that are either on the surface or just under, which root at the nodes, forming colonies. This is also an introduced species.
Above: Panicles of Redtop. Drawing by Agnes Chase from Norman C. Fassett's Grasses of Wisconsin
Below: Spikelets in flower. Leaf sheath and ligule area.
Below: Spikelet branches of the panicle.
Below: The short leaf of Redtop. There are few on the stem, more toward the base.
Below: Underside of the leaf blade and the root system.
Notes: Redtop, while not native, is naturalized in the Garden. Eloise Butler may have catalogued it in her early Garden Records. She listed only the genus name in 1914. There are 3 species known to exist in Hennepin County where the Garden is located - A. perennans, Autumn Bentgrass and A. scabra, Rough Bentgrass - both native - and our species A. gigantea. Redtop is not native but widely naturalized throughout North America. In Minnesota it is found in all but 11 widely scattered counties.
There are five species of Agrostis known in Minnesota, 3 native and 2 introduced. Eloise Butler introduced a different species in 1917, A. glauca and Martha Crone introduced another different one - A. grandiflora in 1947. Neither are native to the state and have not survived.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"