Nature of Competition Several different approaches have been tried to test for allelopathic competition by perennial pepperweed and to identify the substances involved. Perennial pepperweed appears to successfully compete with other plant species for moisture, nutrients, and light. Taxonomic Affiliations Lepidium is well represented in western North America where the genus is represented by approximately 75 species. Many are annuals, but there are several perennial species. None of the native species have the aggressive, invasive behavior or form the dense, robust colonies associated with perennial pepperweed.
Farmers often refer to perennial pepperweed as tall whitetop.
Hoary cress is an invasive alien weed, widely distributed in hay fields and native meadows throughout the Intermountain Area. Hoary cress is much smaller in stature with gray, scruffy leaves compared to the robust, vivid green of perennial pepperweed. Type Of Habitats Invaded Perennial pepperweed has invaded riparian areas along the lower reaches of many river systems in the western United States. It is also found in coastal salt marshes in California. The riparian ecosystems where this weed has spread were often not in good ecological condition before the invasion.