Tall Whitetop (Lepidium latifolium)

Tall Whitetop (Lepidium latifolium)

Links

• http://www.blm.gov/nstc/resourcenotes/rn76.html www.blm.gov/nstc/resourcenotes/rn76.html -- USDA / BLM / NSTC Resource Note NO. 76 Date 01/19/05 -- Background:

The Weed Science Society of America has designated perennial pepperweed as the official common name for Lepidium latifolium L. In the San Luis Valley of Colorado, nearly everyone refers to the plant as ironweed. Throughout much of the western United States the plant is known as tall whitetop. Unfortunately, another weed commonly called “whitetop” is widely distributed on rangelands. The scientific name of this whitetop is Cardaria draba [L.] Desv. and the accepted common name is hoary cress. This may seem confusing, but it results in a communication rather than an identification problem. If correspondence arrives reporting a “whitetop” problem at a field location, it is necessary to determine the exact species that is being referred to as the problem. In the field, it is generally easy to distinguish between Lepidium latifolium and Cardaria draba.

Both weeds known as whitetop are members of the Brassicaceae, or mustard, family. They both have the typical, four-parted mustard flower with white petals. Both species have vigorous creeping roots. These roots have buds that can produce either shoots or roots, and both species form colonies. With all these shared characteristics it would seem that tall whitetop and whitetop are difficult to distinguish. The adjective “tall” is the key. Whitetop (hoary cress) can color entire meadows with a dazzling display of white flowers, but a month later the leaves dry on the fragile 1- to 1.5-foot-tall stems and the plants virtually disappear. Tall whitetop (perennial pepperweed) plants can easily reach heights of 6 feet or more and the stems are semiwoody at the base. Tall whitetop forms thickets that are visible all seasons of the year and the dead plant material persists for several years (Figure).