Conyza canadensis


Horseweed (Conyza canadensis) is a native herbaceous annual in the Asteraceae and was once Erigeron canadensis. Other common names include Canadian horseweed, Canadian fleabane, coltstail, marestail, and butterweed. The leaves are alternate, simple, and with pinnate major veins. The leaves are linear and sessile. The flowers are in heads, and the heads are in terminal panicles. The flowers have five petals and five stamens, and the pappus is composed of capillary bristles. The cream-colored, small (less than 3 mm) ray flowers are pistillate, and the yellow disc flowers are perfect. The ovary is inferior, and fruit is an achene. In traditional North American herbal medicine, horseweed was boiled to make steam for sweat lodges, taken as a snuff to stimulate sneezing during the course of a cold and burned to create a smoke that warded off insects. It is a major weed in much of the United States and is reported as the first weed to have developed roundup resistance. Lots of this species on Allen Acres. Closeup flower picture by the late Ken Wilson in the Louisiana Wildflower Guide. Caterpillars of Blackberry Looper Moth, Common Eupithecia, Variegated Cutworm Moth, yellow-striped Armyworm Moth, Wavy-Lined Emerald, and Evergreen Bagworm Moth are reported to eat this plant. There are two other species in the genus; Conyza bonariensis is a less common non-native species and Conyza ramosissima is even less common but is a native.