Desmanthus illinoensis (Michx.) MacM. ex B.L. Robins. & Fern.
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Basis for Listing
Desmanthus illinoensis is widespread but sparsely distributed in parts of the Midwest and the southeastern United States (Latting 1961). It occurs in different habitats in different parts of the country, but the most common habitat seems to be prairies of one sort or another. Minnesota does have prairie remnants, but most records of D. illinoensis from Minnesota are from shores of shallow prairie lakes rather than actual prairies.
Full-grown specimens of D. illinoensis can reportedly reach a height of 2 m (6.6 ft.) in Oklahoma (Latting 1961), but rarely get more than 1 m (3.3 ft.) high in Minnesota. The plant usually has 2-6 stems which arise from overwintering buds on the root crown just below the soil surface. The stems are loosely spreading and somewhat lax in form, resulting in an open crown.
In most parts of its range, D. illinoensis is considered a plant of tall grass prairies (Latting 1961). However, of the 25 documented occurrences of D. illinoensis from Minnesota, only three are from actual mesic prairies. The others are from sandy lake shores. The lakes where it has been found are within what was historically the prairie region of the state, so there is a prairie connection. Actually, it is quite possible that the species was more widespread in Minnesota prairies but has since declined to the point where populations now only survive along lake shores where they have found refuge from the effects of agriculture.
Biology / Life History
It is known that D. illinoensis is a perennial plant with a large, rapidly developing root system that becomes tough and woody with increased age (Latting 1961). How long any given plant might live is unknown, but the root of one plant reported from Oklahoma had six annual rings (Latting 1961). As in most legumes, the roots of D. illinoensis form nodules that host Rhizobium bacteria in a mutualistic relationship. These bacterial symbiots fix atmospheric nitrogen that is taken up by the plant, which likely gives it an advantage in nitrogen-poor habitats such as sandy lake shores.
Conservation / Management
Compared to prairies, lake shore habitats are probably safer from things like herbicide application and the heavy machinery that accompanies agriculture. And yet, that narrow band of shoreline habitat that encircles all lakes is extremely fragile, and prairie lakes are perhaps the most fragile of all. Lakes in the prairie region are often used as drain basins for agriculture. This means ditches and tile lines dump large amounts of surplus water into lakes after spring snow melt and summer rains. One result is extreme fluctuations of water levels called bounce that happen throughout the growing season. This causes unnatural levels of shoreline flooding and erosion, which native shoreline plants are not adapted to handle. In an attempt to mitigate the damage to shorelines, people often plant the highly invasive Phalaris arundinacea (reed canary grass), or bury the shore under a layer of rock (a practice called rip-rapping). Both these practices are highly damaging to the native species of the shoreline, including D. illinoensis.
Conservation Efforts in Minnesota
Desmanthus illinoensis is known to occur in several Wildlife Management Areas and Waterfowl Production Areas. However, no known attempt has been made to assess the conservation needs of this species within these areas or to determine the effects of current management on its status.
Latting, J. 1961. The biology of Desmanthus illinoensis. Ecology 42(3):487-493.
Wheeler, G. A., Dana, R. P., and C. Converse. 1991. Contributions to the vascular (and moss) flora of the Great Plains: a floristic study of six counties in western Minnesota. The Michigan Botanist 30:75-129.