Parthenium integrifolium L.
Basis for Listing
This long-lived prairie species reaches Minnesota at the extreme northwestern edge of its range. It was apparently limited to only a small portion of southeastern Minnesota (Oak Savanna Subsection and Paleozoic Plateau Section) before European settlement, but it was abundant where it occurred. Parthenium integrifolium (wild quinine) suffered a dramatic decline when the prairies were converted to crop production. In fact, there are believed to be fewer than 200 ha (494 acres) of suitable habitat remaining today, compared with the original habitat of more than 200,000 ha (494,200 acres) (Minnesota’s Remaining Native Prairie). Other prairie states have reported a similar decline, but the species appears to be secure in the East, where it has adapted to marginal habitats that are not heavily exploited for agricultural purposes.
Parthenium integrifolium is a tall robust plant that is quite conspicuous when in full flower. The numerous small heads form a distinctive flat-topped floral structure with densely crowded whitish wooly flowers. In a vegetative state, the species can generally be identified by the basal leaves, which are thick, rough, toothed, and long-stalked. The stem leaves are also toothed, and they are alternate on the stem, becoming increasingly smaller with shorter petioles (stalks) near the summit, eventually becoming sessile (losing the petiole altogether).
In Minnesota, P. integrifolium is restricted to mesic habitats in remnant prairies and savannas of the type that developed in the southeastern portion of the state. It is often found in association with other listed prairie species such as Arnoglossum plantaginea (tuberous Indian plantain), Asclepias sullivantii (Sullivant's milkweed), and Silphium laciniatum (compass plant).
Biology / Life History
Parthenium integrifolium is a long-lived herbaceous perennial. Few details about its life history have been reported in the botanical literature. However, structural details of the plant indicate the flowers are insect-pollinated and seeds are likely dispersed short distances by the wind and possibly in the fur of mammals. Very little is known about the demographic or genetic structure of populations, so it is difficult to speculate about the viability of very small populations or the best way to evaluate management practices.
Conservation / Management
Parthenium integrifolium seems to be intolerant of herbicides, cattle grazing, and repeated haying. Cattle grazing must be carefully managed to prevent over-grazing, which can result in a loss of native biological diversity and the extirpation of certain sensitive species. It can also create conditions for invasion by non-native plant species that displace native species and negatively affect ecosystem processes. Prescribed fire can be a useful tool to control invading brush and reduce thatch, but the timing is critical. The small patches of prairie that remain can be safely burned only during the dormant season, usually in early spring before the native prairie species appear above ground. With such a prescribed fire regimen, an increase in flowering stems of P. integrifolium can be expected (Anderson et al. 2017). Annual hay mowing presents another potential challenge. Seeds of P. integrifolium, like those of most prairie plants, mature in late summer and autumn. If the prairie is mowed before the seeds mature, the species is prevented from producing and dispersing seeds, which can eventually lead to a population collapse.
Best Time to Search
The best time to search for Parthenium integrifolium is when flowers or fruits are present, from mid-June through mid-September.
Conservation Efforts in Minnesota
Parthenium integrifolium occurs in three Scientific and Natural Areas that are being managed for the perpetuation of rare native plants and natural features.
Welby R. Smith (MNDNR), 2020
(Note: all content ©MNDNR)
References and Additional Information
Anderson, R. C., M. R. Anderson, and E. A. Corbett. 2017. White-tailed deer (Odocoileus virginianus) and fire effects on flowering diversity of tallgrass prairie forbs. Journal of the Torrey Botanical Society 144(3):243-253.
Rollins, R. C. 1950. The Guayule Rubber Plant and its relatives. Contributions from the Gray Herbarium of Harvard University No. 172:3-72.
Strother, J. L. 2006. Parthenium. Pages 20-22 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 21. Oxford University Press, New York, New York.