Whitetop
Common Name(s):
Hoary Cress
Growth Characteristics: Whitetop is a perennial forb with a spreading root system from which many aerial shoots, 6-24 inches tall, are produced. The majority of its biomass (up to 76%) is below ground, giving is a highly competitive root system. Because of this, whitetop is more likely to spread vegetatively than by seed. Rosettes are formed in the fall, and overwinter as such, then flower the following spring.
Flowers: Inflorescence is composed of numerous small flowers with petals about 0.1 inch long arranged in flat-topped, sometimes rounded cluster. Although the primary form of propagation is vegetative, a single whitetop plant can produce upwards of 5000 viable seeds.
Fruits/Seeds: Fruits are heart-shaped silicles. The seeds have a mucus-like covering when wet, which helps them stick to the soil surface and aids in germination under low moisture conditions.
Leaves: Leaves are 0.5 – 4 inches long and up to 1.5 inches wide. Basal leaves form a rosette and tend to be more slender, but larger than stem leaves. They narrow into a short petiole. The upper leaves clasp the stem.
Stems: Sprawling to erect, sparsely to densely hairy.
Roots: Deeply penetrating vertical and lateral roots with thick, corky bark, large food reserves, and numerous underground buds from which rhizomes and above ground shoots arise. In addition, plants can also develop from root fragments which are buried in the soil.
Whitetop is primarily a weed of agricultural lands and disturbed sites such as roadsides and railways. It often migrates from cultivated field to adjacent semiarid upland sites. It is found at elevations up to 8800 feet in
Plants contain phytotoxic chemicals that may inhibit germination and initial seedling growth of other plants in natural environments.
Soils: .Whitetop occurs on a variety of soil types, but is most common on soils with neutral to alkaline pH. It is often found on saline soils where moisture is in moderate supply, and especially abundant under irrigation.
Associated Species: Widespread, but does include big sagebrush, crested wheatgrass, and Tamarisk
Due to its extensive underground root system, whitetop is likely to survive severe fires.
Domestic sheep, goats, and cattle may eat whitetop, especially during early growth stages of the plant. Cattle may also eat large quantities of seedheads in late summer, when more palatable forage is no longer available. Viable seeds may be passed in the feces of livestock.