Answer / Justification:
Has no innate dispersal mechanism, but is thought to be spread along interstates by vehicles, by wind tunnels created by paved roads, and on mowing equipment. In some areas may be spread by birds and with horticultural use (The Effects of Fertilization and Time of Cutting on Regeneration and Seed Production of Dipsacus laciniatus (Dipsacacae)). Highways facilitate dispersal of this species (Cutleaf Teasel (Dipsacus laciniatus): Seed Development and Persistence). Dispersal along roads and waterways has been important to teasel spread in North America. On the Lincoln National Forest in central New Mexico, all common teasel populations in habitats occupied by the threatened endemic, Sacramento Mountain thistle (Cirsium vinaceum), occurred adjacent to roads (P<0.0001). In Missouri, teasel populations have "skyrocketed" since the early 1990s. Populations have spread primarily along highways, and researchers suggest that right-of-way mowing operations have been important to seed spread. Since about 1965, cut-leaved teasel spread from New York throughout the Midwest, and much of this spread has occurred along major roadways. By about 1980, cut-leaved teasel was rapidly spreading throughout the Midwest. In Illinois, areas with no or few cut-leaved teasel plants supported large populations in 5 to 10 years. Cut-leaved teasel was first reported in Missouri in 1980, and by about 1990, occurred in 24 Missouri counties. Populations were most common along Interstate 70 (EOL). Teasel seeds are not morphologically adapted for wind dispersal. In a field in Kalamazoo County, Michigan, 99.9% of common teasel seeds fell within 4.9 feet (1.5 m) of the parent plant. Water and human activities are the most likely methods of long-distance teasel seed dispersal. Long-distance teasel seed dispersal by water is likely. Common teasel seeds floated in water for 22 days without losing viability. Along busy roadways and mowed areas, teasel seed may dispersal 2 to 3 times farther than the maximum passive dispersal distance of 4.9 feet (1.5 m). In a natural area near Clinton Lake, Illinois, just 1.3% of cut-leaved teasel seeds made it to the farthest seed trap, which occurred 15 feet (4.5 m) from the source population. Along a nearby interstate, 3% of cut-leaved teasel seeds dispersed 20 to 49 feet (6-15 m) from the source population. In the Mascoutin Recreation Area of DeWitt County, Illinois, the size of mowed cut-leaved teasel patches increased by 360 feet² (33 m²) and unmowed patches increased by 45 feet² (4.2 m²) after 2 years of mowing. In mowed areas, 95% of cut-leaved teasel seed dispersed within 20 feet (6 m) of the source population and more than 1% dispersed more than 30 feet (10 m) from the source (EOL). While animals and water may be infrequent mechanisms for long-distance dispersal, the bulk of the evidence seems to indicate that gravity is the primary mechanism for natural dispersal (besides roadways), and this only occurs near the parent plant. Dispersal along roadways is also not long-distance, but only up to 3 times further than natural dispersal (so 4.5 m).