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Hoary Alyssum

Hoary Alyssum

 (Berteroa incana)



Common Names:

Hoary False Madwort, Hoary False Alyssum



Hoary Alyssum is an annual, biennial, or perennial in the mustard family and can grow up to three feet tall. It is a newer listing to the Montana state list and is believed to be a plant that became more pronounced and invasive due to the recent drought in most of southern Montana. Leaves in the rosette are long-stalked and broader near the tip. Upper leaves are stalkless and taper to a long narrow point. All leaves are alternate, have smooth margins, and do not clasp the stem. All parts of the plant are covered with short, star-shaped hairs with give the plant a silver- grayish appearance. Stems are also a grayish-green in color. The flowers are similar to other mustards in that they are small, deeply lobed and have white petals. They are produced in long racemes along the stems. The plant flowers from early June until fall. Small, oblong, flattened seed pods appear along the stem and each seed pod can contain two to six brown seeds. This tap rooted plant reproduces only by seed.


Key Features:

Flowers are small and white with 4 petals; they are deeply divided and formed in racemes along the stem. It is distinguished from other mustards by its stalkless, non-clasping stem leaves that have smooth edges and the dense star-shaped hairs that give the whole plant a “hoary” appearance.



It is particularly adapted to dry conditions such as occur on sandy or gravelly soils. It is invasive along roads, railroads, trails, gravelly stream and lake banks, in lawns, farmyards, vacant lots, overgrazed pastures and rangeland, and in hay meadows.


Currently found in the following counties:

Beaverhead, Big Horn, Broadwater, Carbon, Cascade,Chouteau, Deer Lodge, Flathead, Gallatin, Glacier, Jefferson, Lewis & Clark, Liberty, Madison, Meagher, Mineral, Missoula,  Park, Powell, Ravalli, Silver Bow, Stillwater, Treasure, Yellowstone



  • Herbicide

  • Pulling

  • Cultivation


Interesting Facts:

Because of an old belief that they cured rabies, the alyssums have been called madwort or heal-bite. Hoary alyssum is toxic to horses and remains toxic in cured hay. Horses experience lameness and consumption of large amounts of this plant can result in dehydration, diarrhea and cause abortions. However, if treated early, most horses recover.


Commonly Confused Plants:

  • Rosettes are often confused with Crepis tectorum, Arabis divaricarpa, Arabis glabra, and Arabis hirsute.

  • Whitetop

  • Perennial pepperweed




Photo Credits: Brian Ostwald; Matt Lavin; Kellieanne Morris; Matt Lavin; Kellieanne Morris


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