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Hoary Cress, Whiteweed, Peppergrass, Heart-Podded Hoarycress, Hoary Cardaria
The perennial Whitetop is another member of the mustard family and can grow up to two feet in height. Roots are extensive and deeply penetrating, both laterally and vertically. Small buds on the roots create new shoots. Leaves are grayish-green in color, upper leaves clasp the stem and can be up to four inches long. They are shaped like arrow heads, are finely toothed, and soft as they are covered with fine hairs. Leaves at the base of the plant form a rosette early in the spring and are larger than the leaves on the stems. Flowers are white with four petals, ¼ inch across and shaped in a cross. They are one of Montana’s earlier invaders and bloom from late April to early June. Flowers form clumps at the ends of the stems and give the plant a flat-topped appearance. Flowers tend to get a cream colored cast as they mature. Seed capsules are flat and heartshaped with two reddish, brown seeds encased in pods. Whitetop reproduces by seed and by root, and each plant can produce around 3,000 seeds annually.
Look for a flower cluster that is flat-topped and white to cream colored. Leaves and stems have a grayish- green color and leaves are soft and covered in fine hairs.
Whitetop prefers open, unshaded areas and can be found on a wide variety of soil types. Whitetop generally grows better in moist sites or areas of moderate rainfall. Its attraction to moisture results in it being found in sub-irrigate pastures, ditch banks, irrigated cropland and at the edge of riparian areas. Whitetop prefers disturbed sites, including excessively grazed areas, waste areas, roadsides, and open grasslands.
Currently found in the following counties:
Beaverhead, Big Horn, Blaine, Broadwater, Carbon, Cater, Cascade, Chouteau, Custer, Dawson, Deer Lodge, Fallon, Fergus, Flathead, Gallatin, Garfield, Glacier, Golden Valley, Granite, Hill, Jefferson, Judith Basin, Lake, Lewis & Clark, Liberty, Lincoln, Madison, McCone, Meagher, Mineral, Missoula, Musselshell, Park, Petroleum, Phillips, Pondera, Powell, Ravalli, Richland, Rosebud, Sanders, Sheridan, Silver Bow, Stillwater, Sweet Grass, Teton, Toole, Valley, Wheatland, Wibaux, Yellowstone.
In the Pacific Northwest with abundant rainfall, roots have been shown to occur up to thirty feet in dept. Seed may have been in the soil that was used as ballast for sailing ships, as it was first discovered around seaports on the coasts of the U.S.
Commonly Confused Plants:
Perennial Pepperweed (Lepidium latifolium)
Photo Credits: Brian Ostwald; Chris Evans, River to River CWMA, Bugwood.org; K. George Beck & James Sebastian, Colorado State University, Bugwood.org; Bob Osborn, Yeovil, England, www.wbdpublications.co.uk; Zack Taylor