Introduced Species of California Common Teasel

¶ … Species of California (Common Teasel)

The Common Teasel (Dipsacus fullonum) is a plant species identified by several alternate names, including wild teasel, Indian teasel, card teasel, card thistle, gypsy-comb, Venus-cup, and finally Fuller's teasel. With the exception of the great plains region in the north, it can be found growing wild throughout the continental United Staes and parts of Canada. Fuller's teasel is actually a cultivated variety (Dipsacus sativus), which is often confused with its wild form, the common teasel. The teasel is not native to California, having originated in Eurasia and Northern Africa and proliferated accidentally during the eighteenth century as a contaminant in imported seed stocks and in flower arrangements. The cultivated teasel variety was used as an ornamental item in dried flower displays, as well as a hairbrush, and for creating wool. Common teasel is classified in the United States as a noxious invasive species that is rated as moderately problematic to native ecosystems. This occurs primarily when it grows into high-density stands that obstruct the movement of humans or domestic animals. It is occasionally referred to as a "bio-bully" species. Common teasel occurs most often in riparian or wetland areas, but has adapted over the past thirty years to flourish in open non-wetland areas with abundant sunshine, and is commonly observed along highways, grassy meadows, cemeteries, and disturbed sites at elevations ranging from sea level to 5500 feet (Calflora).

Fuller's teasel was a reference to the puckered appearance of the leaves. The name was derived from the archaic verb to full, which referred to a process used to thicken and shrink cloth using heat, moisture and pressure. The prickly fruit of the D. sativus variety was also used to raise the nap on woolen fabrics. This process was called teasing wool, which resulted in the name teasel for the family of plants. The tradespersons who carried out this craft were known as fullers, giving rise to the name of the common teasel's progenitor (Reeves).

The common teasel (hereafter referred to as "teasel") is a monocarpic biennial plant, which means that its typical two-year life cycle ends after it has flowered and set seeds. It will then sprout once again as a new plant. (Gucker). Following germination, the plant has a rosette form with the leaf bases fused together to form a cup, which surrounds the stem and collects rain water. The name dipsacus originated from this feature, derived from the Greek word dipsa, meaning "to thirst." The leaves have a puckered appearance, with ribbed edges and small spines along the middle of the underside of each leaf (Reeves).

In the one to two years following germination, the plant grows a flowering, prickly stem which can be from two to eight feet in height. The flowers are purple or lavender to white in color, small in size and arranged in dense conical formations called heads, three to ten centimeters in length consisting of up to 1,500 flowers each. Between the flowering and seed-producing stages, the stems become woody, with branches appearing in the upper part of the plant. The flowering season for teasel varies slightly according to its location. In California, flowering takes place between the months of April and August, and is delayed by one to three months in the midwestern and Northeastern states. The flowers are pollinated by insects, and seeds mature during the Fall. Seed dispersion occurs in several ways. The majority of seeds fall near the base of the plant, but can be transported over several weeks to greater distances, carried by wind, moving water and soil, animals, and human activities such as mowing. The seeds themselves are capable for surviving for over five years before germinating, and individual stands of teasel may thrive and persist for two or more decades. The underground structure of the teasel consists of a thick and fleshy tap root system descending to a depth of two to three feet below ground (DiTomaso et. al.).

Teasel is an aggressive species with no natural enemies or consumers to temper its growth and proliferation. If it is permitted to establish itself in savannah or prarie regions, it can easily thrive and become dominant by out-competing other, native species of vegetation. A single teasel plant can produce more than two thousand seeds in its life cycle, and each seed is capable of remaining dormant in the ground for two years or more before germinating. Seed germination rates are typically high, in the range of 30-80%. Due to their similarity in growth patterns, teasels have been compared to dandelions as invasive species ("Invasive species").

Management of unwanted teasel growth can take the form of mechanical or chemical controls. Cutting, extraction and burning are common mechanical solutions. Small teasel infestations can be controlled by trimming the plants below the crown. Large infestations in crop growing areas can be managed by trimming the plants while they are still young, in the rosette stage. Seed production can be thus prevented by preventing the plants from reaching the flowering stage. Due in part to the generally moist habitats teasel tends to grow, burning is a difficult method of control for this species. Even in non-aqueous growth areas, the high density of teasel rosettes and stalks limits the ability of fire to spread, or to achieve temperatures sufficiently high to be lethal to plant tissues. Furthermore, burning methods are impractical along roads and highways with vehicular traffic, which are common areas of infestation (Gucker).

Herbicide-based solutions also exist, but are limited in their effectiveness and therefore less commonly used. Herbicidal chemicals including Triclopyr or Glyphosate can be applied to teasel leaves and stems at a 2% concentration level. This method can be effective if applied in advance of the plant reaching the bolting or flowering stalk stage. If the herbicide is applied after this stage, limited control may be possible but seed production may still occur, rendering this a temporary or partial solution. As teasel tends not to grow back if it is removed before the seed-setting stage, cutting is the preferred method of control, where practical and possible (DiTomaso et. al.).