Rare Species Guide

  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.

In spite of Minnesota's reputation as the land of 10,000 lakes, most of the shallow prairie lakes in the state were drained to create farm fields. Much of the drain water was routed to other lakes that were in basins too deep to drain. As a result, very few prairie lakes have been left in a natural condition. Evidence suggests that only lakes with a minimal amount of disruption can sustain populations of D. illinoensis. This puts the species in a precarious position and prompted the species' designation as a special concern species in 1984.

  Description

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.

The leaves are bipinnately compound, averaging about 8 cm (3.1 in.) long and 4.5 cm (1.75 in.) wide. Each primary division of the leaf contains 10-14 secondary divisions, and each secondary branch has 13-31 pairs of tiny leaflets, giving the entire leaf a distinctive feathery appearance. The leaflet pairs close together in the evening and remain closed until the following morning when they open again, but the leaves are not touch-sensitive (Latting 1961).

The small, white flowers are arranged in round heads. Each head has an average of about 50 flowers and measures about 1 cm (0.4 in.) across. The heads are borne at the ends of upright stalks 2-5 cm (0.75-2.0 in.) long. These stalks are strongly angled in cross-section and originate in the axils of the leaves. Each flower has a single style and about 5 stamens, which extend some distance beyond the corolla. The calyx of the flower is tubular and no more than about 2 mm (0.08 in.) long. The corolla consists of 5 greenish white petals about 3 mm (0.12 in.) long (Latting 1961).

Each seed capsule is beaked and strongly curved, spiraling around the receptacle to form a loose head. Each capsule has 1-7 (usually 5), shiny brown seeds that average 4 x 3 mm (0.16 x 0.12 in.) in size (Latting 1961).

  Habitat

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.

The leaves are a deep green color during the summer, but they turn brown and drop early in the fall season leaving conspicuous bare stalks with brown fruits. The seeds are able to germinate easily as soon as they reach maturity. However, seeds that do not germinate quickly develop an impermeable seed coat and enter a dormant state. Scarification is needed to break dormancy and stimulate germination (Latting 1961).

One reported study in Oklahoma concluded that D. illinoensis is preferentially grazed by cattle (Latting 1961). The same report concluded that repeated and continuous grazing by cattle over an entire season will seriously harm populations of this plant, but mowing once or more during the season apparently had the potentially beneficial effect of greater vegetative growth and a longer flowering period.

Desmanthus illinoensis is distinctive throughout the growing season, so searches can be conducted anytime between about the first of May and the middle of September.

  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.

  References and Additional Information

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.