NPS Photo

Horseweed

Conyza canadensis var. glabrata

Family: Asteraceae (A Utah Flora – Compositae) – Sunflower Family

Annual herbs from taproots with watery juice; 2' to 4.3' (0.5 to 13 dm) tall

Leaves: alternate; simple; 0.8” to 4” (2 to 10 cm) long, 0.8” to 3.2” (2 to 8 cm) wide

Flowers: white or purplish small ray flowers and yellow disk flowers; ray flowers 0.02” to 0.04” (0.5 to 1 mm) long; 8 to 21 disk flowers, perfect, fertile, about 0.004” (0.1 mm) long; flower head appears to be a single flower, but is composed of several flowers (a composite). 25 to 40 female (pistillate) flowers

Pollinators: bees and flies

Fruits: achene – 1 seeded with hard shell

Blooms in Arches National Park: August, September

Habitat in Arches National Park: weed in riparian and moist disturbed areas

Location seen: widespread

Other: The genus name, “Conyza”, is from the Greek “konops” meaning “flea”, used by Pliny (an author and natural philosopher) as a name for a fleabane. The species name, “canadensis”, means “of or from Canada and North America” and refers to its distribution. The variety name, “glabrata”, means “somewhat glabrous (without hairs or smooth)”.

This family is the most advanced and complex of the dicots. The family is rich in oils and resins and is found in every part of the world, but is infrequent in the tropical rainforest. Aquatic or semi-aquatic species are also uncommon.