Purple prairie clover

Appearance

Dalea purpurea is a perennial herb growing 20 to 90 cm tall. The mature plant has a large taproot 1.7 to 2.0 meters deep. The stem is woody with several branches. The leaves are a few centimeters long and are divided into 3 to 7 narrow leaflets. The inflorescence atop each stem branch is a spike up to 7 cm long containing many purple flowers. The fruit is a legume pod containing 1 or 2 seeds.

Naming

Dalea purpurea Vent.
Dalea violacea (Michx.) Willd.
Kuhnistera violacea (Vent.) Steud.
Petalostemon violaceum Michx.
Petalostemon pubescens (A.Gray) A.Nelson
Petalostemon purpureum (Vent.) Rydb.
Petalostemon standleyanus Rydb.
Psoralea purpurea (Vent.) MacMill.

Distribution

It is native to central North America, where it occurs from central Canada to the southeastern and southwestern United States, except for the east and west coasts. It is a common and widespread plant within its range, especially on the Great Plains. In 1804, Meriwether Lewis collected a specimen in Nebraska.

Status

Kentucky - Special Concern
Michigan and Ohio - Probably Extirpated
Tennessee - Endangered

Behavior

The nectar and pollen of the flowers attract many kinds of insects, including honeybees, bumblebees, cuckoo bees (Triepeolus spp., Coelioxys spp.), long-horned bees (Melissodes spp.), leafcutter bees (Megachile spp.), Halictid bees (including green metallic bees), plasterer bees (Colletes spp.), Sphecid wasps, Tiphiid wasps, Syrphid flies, bee flies (Bombyliidae), thick-headed flies (Conopidae), small butterflies, skippers, and beetles (Robertson, 1929; Reed, 1993, 1995). The following plasterer bees are oligoleges (specialist pollinators) of Dalea spp. (prairie clovers): Colletes albescens, Colletes robertsonii, Colletes susannae, and Colletes wilmattae.

Habitat

This plant is adapted to a habitat with periodic wildfires. In some areas, it depends on fire to clear encroaching woody vegetation, as it cannot tolerate shade.

Dalea purpurea is a common member of the flora on the plains of central North America, occurring in a variety of habitat types, including several types of grassland. It occurs in glades, riverbanks and floodplains, oak woodlands, pinyon-juniper woodlands, shrubsteppe, many types of forests, and the Sand Hills of Nebraska. It occurs in a variety of prairie ecosystems. On tallgrass prairie it is associated with plants such as little bluestem , big bluestem , prairie Junegrass , prairie dropseed , lead plant , and silky aster . On midgrass prairie it grows alongside several grasses such as silver bluestem, purple threeawn, sideoats grama, and sand dropseed. On shortgrass prairie it is associated with grasses such as blue grama , hairy grama , and buffalo grass . This species may be considered an indicator of pristine prairie.

Reproduction

By seeds.

Predators

Some insects feed destructively on the seeds, foliage, and other parts of Purple Prairie Clover and other prairie clovers. These species include seed-eating larvae of some weevils (Apion reconditum, Apion tenuirostrum, Apion capitone), seed-eating larvae of a beetle (Acanthoscelides seminulum), a plant bug (Lopidea minor), Three-spotted Treehopper (Vanduzea triguttata), Little Pasture Grasshopper (Melanoplus confusus), and larvae of two butterflies, the Dogface Sulphur (Colias cesonia) and Reakirt's Blue (Hemiargus isola); see Sauer (2005), Boe & Johnson (2014), Kingsolver (2004), Knight (1941), Haarstad (2002), Campbell et al. (1974), and Opler & Krizek (1984). Purple Prairie Clover is palatable and high in protein, therefore mammalian herbivores of all kinds eat this plant readily. It can be difficult to establish in some areas if there is an abundance of these animals. It is possible that small rodents carry the seeds to their dens, which may aid in the distribution of this plant.

Uses

This species is used for revegetation efforts on reclaimed land, such as land that has been strip mined. It is good for preventing erosion and for fixing nitrogen in soil. Though it is often found in mid- to late-successional stages of ecological succession, it may also be a pioneer species, taking hold in bare and disturbed habitat, such as roadsides.

Purple prairie clover provides food for a number of animals, such as pronghorn. It also grows in cultivated fields and becomes included in hay for livestock. It is nutritious and is "considered one of the most important legumes in native grasslands on the Great Plains." It also had a number of uses for Native Americans. The leaves are edible and good for making tea and medicines, and the roots are palatable when chewed. The stems were used as brooms by the Pawnee people.