Habitat, Spread and Impacts

Habitat

Hoary alyssum is adapted to the temperate continental climate characterized by cold winters and hot dry summers. Fall seedlings and rosettes are resistant to winterkill, and flowering plants are resistant to summer drought. The plant grows well on sandy or gravelly soils with poor soil fertility, and is most prolific on dry, disturbed open sites. It is commonly found on limestone and calcareous substrata and less so on acidic soils. It is common in fields of alfalfa, clover, or birdsfoot trefoil. In Montana it has been found along roads, railroads, trails, and gravelly stream and lake banks, in lawns, farmyards, vacant lots, overgrazed pastures and rangeland, and in hay meadows.

Spread

Hoary alyssum is believed to have been originally transported to North America as a contaminant of clover and alfalfa seed. Contaminations of forage and lawn seed, as well as contaminated hay, are still considered likely means of long distance seed dispersal. Hoary alyssum seed may also disperse long distances on mowers, other machinery, and in contaminated soil and gravel. Seeds disperse through valves in the seed pod. It is believed most seed falls near parent plants. However, the winged margin and light-weight seed may enable wind and water dispersal, and animals consuming the seed pods may disperse seed in their droppings, although there is no information to support this.

Impacts

Hoary alyssum began to increase in hay fields and pastures in the 1950s and 1960s, particularly under conditions of drought, overgrazing, or poor soil fertility. It decreases forage value because the woody stems of mature plants are low in crude protein and digestible carbohydrates. Contamination of 30percent or more of forage with hoary alyssum is toxic to horses causing laminitis, limb edema, diarrhea, intravascular haemolysis, and hypovolemic shock. Its ability to persist under dry conditions and its continuous flowering and fruiting enables it to compete with native plants on range and wildlands and reduce biodiversity. In Minnesota it has been implicated in the reduction in species richness of pollinator communities because it attracted a minimal number of pollinating insects.

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Last Modified: 11/18/2008