General: Celery Family (Apiaceae). Daucus pusillus is a native annual found most commonly during the early-mid part of the growing season. In most parts of Texas, this species has gone to seed by mid-summer. Rattlesnake-weed resemble their cultivated relative, the garden carrot. The stem is normally slender, from 2-4 feet in height and unbranched or only a single weak branch as compared to the introduced Daucus carota, which is sometimes heavily branched and more robust. The flower is a white umbel. Upon maturity, the flower cluster (umbel) closes to form a cup or bird’s nest. The leaves are pinnately compound and finely cut. Leaflets are deeply serrated (saw-toothed). The seed of Daucus carota have fine hairs rather than the stiff bristles common to Daucus pusillus. Another distinguishing characteristic between the two species is the central flower of each individual umbellet is rose or purple in Daucus carota rather than being white throughout as found in Daucus pusillus.

American wild carrot is self-fertile. The flowers are hermaphrodite, having both male and female organs, and are pollinated by flies and bees.

A similar species is water parsnip (Sium suave), which has a corrugated main stem and leaves only once compound. Bishop’s weed (Ammi majus) and water hemlock (Cicuta maculata) have white umbels, but the leaflets are not deeply serrated or carrot like.