One-Flowered Broomrape
Orobanche uniflora
Broomrape family (Orobanchaceae)

Description: This wildflower is a perennial, producing 1-5 erect flowering stalks about 3-8" tall. The flowering stalks are produced by a scaly short stem that is 1" or less in length; this stem is usually underground and only the flowering stalks are visible above ground. The short scales along the stem are highly modified leaves; they are oval to ovate in shape and somewhat thick and succulent. The flowering stalks are usually pale gray or grayish tan, terete, and hairy. At the apex, each stalk produces a single nodding flower about –1" long. This flower has a tubular corolla with 5 spreading lobes and a short hairy calyx with 5 lanceolate teeth; the teeth usually have slender tips. The coloration of the calyx is usually similar to the flowering stalk. The corolla is white to lilac or a blending of these two colors (rarely is it purple, at least in the Midwest); it is covered with short fine hairs. Along the lower throat of the corolla, there is usually a patch of bright yellow hairs, although sometimes these hairs are cream-colored or white. Inserted within the corolla, there is an ovary with a single style and 4 stamens. The blooming period occurs from late spring to early summer and lasts about 2-4 weeks. In the absence of cross-pollination by insects, the flowers are self-fertile. Each flower is replaced by an ovoid seed capsule, that splits open to release minute seeds. These seeds are small enough to be blown about by the wind and they eventually sink into the crevices of the soil and ground litter. The root system is parasitic, developing feeder roots (haustoria) that attach themselves to the roots of a suitable host plant. One-Flowered Broomrape is holoparasitic and lacks chlorophyll; it is dependent on the host plant for nutrients.

Cultivation: This wildflower is often found in moist rocky areas where there is some protection from the wind. However, it is also found in non-rocky soil. The presence of a suitable host plant is required before the seeds will germinate. The seeds germinate in response to the presence of chemicals in the soil that the developing host plant produces. In addition, a suitable fungus may be necessary to function as an intermediary between the seedling and host plant. Suitable host plants include Sedum spp. (Sedums), upland Saxifraga spp. (Saxifrage), Helianthus spp. (Sunflowers), Solidago spp. (Goldenrods), and probably other plant species. Transplanted specimens of One-Flowered Broomrape are unlikely to survive for very long.

Range & Habitat: One-Flowered Broomrape is occasional in Illinois, except in the SE section, where it is rare or absent. This is the most common Orobanche sp. (Broomrape) in the state; it is native. Habitats include upland woodlands, rocky cliffs where some seepage occurs, the base of bluffs, rocky glades, and thickets. This species is usually found in high quality natural areas.

Faunal Associations: The flowers are cross-pollinated by bumblebees and possibly other long-tongued bees. Charles Robertson (1929) observed the bumblebee, Bombus pensylvanicus, visiting the flowers for nectar. Aside from this observation, very little appears to be known about floral-faunal relationships for this species.

Photographic Location: The photograph (Copyright 2009) of Orobanche uniflora was taken by Lisa Culp in a wooded area of Somme Prairie Grove Nature Preserve in Cook County, Illinois.

Comments: This unusual wildflower has a reputation of appearing unexpectedly in one area, only to disappear and reappear in another area of the same habitat. Most likely, this intermittent pattern results from the underground stems producing flowering stalks during some years, but not others. Unlike some other species in this genus, One-Flowered Broomrape produces only a single flower per stalk, rather than a spike-like stalk with multiple flowers. Only one other species in Illinois, Orobanche fasciculata (Clustered Broomrape), shares this characteristic. Clustered Broomrape has a longer scaly stem (2-4") that is also underground, from which 4-12 flowering stalks develop above ground. There is a tendency for the lobes of its flowers to be less spreading or more divided into 2 lips; One-Flowered Broomrape has flowers with spreading lobes and poorly defined upper and lower lips. The common name of this genus, 'Broomrape,' derives from an Orobanche sp. in Europe that is parasitic on Broom (Cytisus sp.) as a host plant. Other common names of Orobanche uniflora are 'Naked Broomrape' and 'Ghost Pipes.'