Buchloe dactyloides (Nutt.) Engelm.
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Basis for Listing
Although Buchloe dactyloides is common throughout large areas of the Great Plains, it is very rare in Minnesota where it has been listed as a special concern species since 1984. Here it is restricted to rock outcrops in the southwest part of the state and almost exclusively associated with Sioux quartzite bedrock. Almost all of the populations are concentrated in two small geographic areas. One is about 40 km (25 mi.) long and stretches between Luverne, Jasper, and Pipestone; the other (only 16 km (10 mi.) long) is in Cottonwood and Brown counties between Sanborn, Jeffers, and Comfrey. Depending on how you count the clustered observations of B. dactyloides, there are 20-30 known populations. About half of the populations are on land that is in public ownership and being managed for conservation. However, rock outcrops face several threats including overgrazing of livestock and bedrock mining.
Buchloe dactyloides is a low-growing, perennial grass that is gray-green or yellow-green in color. It spreads by stolons (aboveground horizontal stems), which root at their tips, and thus can form a dense mat or sod. The mat of leaves is typically 5-10 cm (2.0-3.9 in.) tall (Hitchcock 1971), and the leaf blades are 2-15 cm (0.8-5.9 in.) long and 1-2.5 mm (0.04-0.10 in.) wide (Snow 2003). Some parts of the leaf have sparse, long hairs (Hitchcock 1971); leaf blades curl when dry (Snow 2003). Male (staminate) and female (pistillate) flowering stems are usually on separate plants and can be 1-30 cm (0.4-11.8 in.) tall (Snow 2003). Staminate stems are generally taller than pistillate stems, and retain their flowering parts into late summer or fall (Great Plains Flora Association 1986), whereas pistillate stems are most visible during flowering in the spring. The staminate flowers are borne in 1-3 short spikes at the tip of the stem above the leaves (Snow 2003). Within each spike, the flower units (spikelets) hang downward in 2 densely crowded rows, in a regular pattern resembling a comb. The pollen bearing part of the stamen is colored brownish, red, or orange (Snow 2003). The pistillate flowers are borne on stems typically clustered in small tufts, with the flowers hidden among the leaves and leaf sheaths (Hitchcock 1971; Snow 2003). Pistillate flowering stems may have 2-3 inflorescence branches, each with a cluster of 1-5 flowers (spikelets) (Quinn and Engel 1986). Some of the outer flower parts are hardened and together the clusters of hardened flower structures make a sort of 'bur' that breaks off at the base and is dispersed as a unit (Hitchcock 1971). Individual pistillate spikelets are 7 mm (0.28 in.) long and 2.5 mm (0.10 in.) wide (Snow 2003), and they have 3 awnlike teeth at the tip (Hitchcock 1971; Snow 2003).
In much of its U.S. range, B. dactyloides grows on clay soils, but in Minnesota, it is associated with southern bedrock outcrops. Bedrock outcrops are open plant communities on horizontal or sloping rock exposures. Lichens are abundant and herbaceous plant cover is sparse to patchy, growing mostly in crevices, shallow soil deposits, and rainwater pools (Minnesota DNR 2005). All Minnesota populations of B. dactyloides are found on Sioux quartzite outcrops except for two. One of these is on granite bedrock of the Minnesota River valley in Lac qui Parle County. The other is in Renville County along a weedy railroad grade where it was first observed in 1992, and may have been fairly recently established. Many railroad beds are constructed of crushed quartzite and B. dactyloides seed could have been brought here from a quartzite quarry or somehow carried in along the railroad tracks.
Biology / Life History
Buchloe dactyloides is a dominant grass on upland, shortgrass areas of the Great Plains (Hitchcock 1971; Snow 2003). It is a very important pasture grass for this region (Hitchcock 1971), providing valuable forage for livestock and wildlife (Snow 2003) even in winter (Hitchcock 1971). It can withstand heavy grazing (Snow 2003), although extreme overgrazing will deplete its root reserves (Weaver 1968 as cited in Huber 1987). In addition to its commercial value as forage, B. dactyloides has also been cultivated and planted for erosion control and as a low maintenance turfgrass (Hitchcock 1971) as it forms a dense sod and keeps such a low stature. Because of its commercial uses, it has been introduced to parts of the U.S. where it is not native. Populations east of the Mississippi River and south of the Ohio River are probably fairly recent introductions (Snow 2003).
Conservation / Management
While B. dactyloides generally tolerates livestock grazing, it is threatened by physical trampling in overstocked pastures. The shallow soil over bedrock is easily churned up by cow hooves. To protect B. dactyloides, and other sensitive species sharing its habitat, cattle stocking rates should be kept low enough to avoid physical breakup of shallow soil patches on the margins and in cracks of outcrops. Another major threat is mining. Changes in federal highway construction standards have increased the demand for crushed bedrock. This, in addition to recent high grain prices, is leading some farmers to seriously consider blasting or quarrying the rock outcrops on their land to make room for more crop fields (Harris 2009). Heavy herbicide use to treat Carduus spp. (thistles) also threatens rock outcrop habitats (Minnesota County Biological Survey 2007). While B. dactyloides should not be directly harmed by broadleaf herbicides (because it is a monocot), other rare species that share its habitat are not so hardy. Particularly sensitive are the aquatic species that occur in temporary rainwater pools on the same rock outcrops including Limosella aquatica (mudwort), Isoetes melanopoda (prairie quillwort), Crassula aquatica (pigmyweed), and Marsilea vestita (hairy waterclover). Two other rare species, Opuntia macrorhiza (plains prickly pear) and Schedonnardus paniculatus (tumblegrass), are also associated with the terrestrial components of B. dactyloides habitat. For the sake of the more sensitive species in these habitats, herbicide application for invasive weed control should consist of spot treatment of individual plants instead of broadcast application via boom sprayers or aerial methods.
Conservation Efforts in Minnesota
A number of sites that support B. dactyloides are owned by public land management agencies and private conservation organizations. Some, perhaps most, of these sites are actively managed in some way, although goals and objectives vary. Unfortunately, the full effects of various management activities on B. dactyloides are not being monitored.
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Hitchcock, A. S. 1971. Manual of the grasses of the United States (2 volumes). Second Edition. Dover Publications, Inc., New York, New York. 525 pp.
Huber, J. K. 1987. Buchloe dactyloides (Nutt.) Engelm. in Minnesota. Unpublished report submitted to the University of Minnesota, Duluth, Minnesota. 21 pp.
Minnesota County Biological Survey. 2007. Native plant communities and rare species of the Minnesota River Valley counties. Division of Ecological Resources, Minnesota Department of Natural Resources, St. Paul. 153 pp.
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Snow, N. 2003. Buchloe. Pages 270-271 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 25. Oxford University Press, New York, New York.
Weaver, J. E. 1968. Prairie plants and their environment. A fifty-year study in the Midwest. University of Nebraska Press, Lincoln, Nebraska. 276 pp.