Grama Grasses (Bouteloua species)

Main Sources: Gould, Frank, 1951, Grasses of the Southwestern United States, Tucson: University of Arizona Press; Shreve, Forrest & Ira Wiggins, 1964, Vegetation and Flora of the Sonoran Desert, Vol. 1, Palo Alto: Stanford University Press; Kearney, Thomas & Robert Peebles, et al, 1960, Arizona Flora, Berkeley: University of California Press; McClaran, Mitchel & Thomas Van Devender, 1995, The Desert Grassland, Tucson: University of Arizona Press; van Devender, Thomas & Mark Dimmitt, "Desert Grasses", in Phillips, Steven& Patricia Comus, eds., 2000, A Natural History of the Sonoran Desert, pp. 265-80, Arizona-Sonora Desert Museum Press, Tucson; Ruyle, George & Deborah Young, eds., 1997, Arizona Range Grasses, Tucson, University of Arizona College of Agriculture; USDA Conservation Districts of Southeastern Arizona,, n.d., Grasses of Southeastern Arizona. Washington, D.C.

Grama grasses are distinctively American, with 40 species, most developed in the Southwestern United States. These are Arizona's most important forage grasses ("Grama" is "grass" in Spanish.). Occurring as both annuals and perrenials, they usually have slender stems with distinctively comb-like flowering spikes.

Side-oats Grama (Bouteloua curtipendula)

Widely distributed throughout North and South America, this perennial warm-season bunchgrass displays tall, slender seed stalks with up to 20 spikes aligned along one side of the stalk, like a line of flags depending from a mast. (Click on image at left to enlarge).

Side-oats is the largest of the grama grasses, sometimes over 30" tall. It is widespread in Arizona, found in our area mostly on rocky open slopes.

Leaves, clustered mostly near the base of the plant, are coarse, stiff, and usually wide and flat, shown below (click on the image to enlarge it)

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The spikelets are awnless or have very short awns. Click on image to left to enlarge.

 

Though its seeds are numerous and effective, Side-oats Grama produces mainly by rhizomes, thus increasing its capacity to stabilize soils.

 

Black Grama (Bouteloua eriopoda)

A perennial spreading bunchgrass reaching 2 feet in height, it is distinguished first by its darker-wooly internodes and second by its 3 to 6 or more slender, narrow (comb-like) and slightly up-curled spikes. Its leaves are narrow, inconspicuous, inrolled and wavy. Click on the image below for closeup of inflorescence.

A tangled, perennial grass, it forms large bunches of wiry stems and spreads by wiry stolons (trailing reproductive stems). It is vulnerable to overgrazing and trampling. In Arizona it is found mostly above 3,500', which explains why we mainly see it in the Northeast corner of Saguaro Juniper lands. This highly nutritious grass has suffered from overgrazing in many parts of Arizona.

Spruce-top Grama (Bouteloua chondrosioides), or Slender Grama (B. filiformis)

These two gramas are hard to distinguish. According to the USDA (cited above), Slender Grama grows on coarser, rockier soils than does the Sprucetop, so many of our grasses may be the Slender species. These gramas are small, fine-stemmed, perennial bunchgrasses, up to 18" tall with bright green color when young. The leaves are very narrow and tending to become curly when mature.

A perennial warm season bunchgrass whose stems are erect and tufted, relatively tall (see image at left, photo near SBS Saddle, Feb. 2004),

with leaves clustered toward the base; leaf sheaths are rounded, not conspicuously flattened. Click on the image below to enlarge.

Each seeding stem has fewer than 10 pendulous, one-sided spikes, which are hairy.

Below, part of a dense stand of Sprucetop Gramma in the wash below the Trail Tank:

Below, arrays of spikes and spikelets (click to enlarge).

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Hairy Grama (Bouteloua hirsuta)

A perennial, warm-season grass, up to two feet tall, whose leaves are fine and narrow, confined to the base of the plant. The seedheads are comb-like and hairy spikes, borne on a leafless stalk and usually 2 in number (though one, three and four are sometimes found). They are usually curved, sometimes coiled into a complete circle, with a slender needle-like point extending beyond each separate spike. Like Black Grama, these mostly grow above our Saguaro Juniper area (4,000 to 6500 feet elevation), but we do see them in the Notch Basin and in our Northeast Corner. They are highly nutritious to browsers, but are also weakened by heavy grazing.

Six-weeks Needle Grama (Bouteloua aristidoides)

This annual grass is aptly named, since its entire life-cycle is compressed into a very brief portion of the summertime. Found from Texas and southern Colorado to Arizona and northern Mexico, it appears to be closely related to the Grama perennials.

 

 

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