Hemp dogbane (Apocynum cannabinum) is a close relative of common milkweed. It is a large perennial weed with opposite leaves and a milky sap, and its stem is highly branched in the upper third to half of the plant. Hemp dogbane can grow 5-6 ft tall and is found throughout much of the United States.
The common name, Dogbane, refers to the plant’s toxic nature, which has been described as “poisonous to dogs.” Apocynum means “Away dog!” and cannabinum means “like hemp,” in reference to the strong cordage that was made by weaving together the stem’s long fibers.
The leaves appear entire, ovate or elliptic, 2-5 inches long, 0.5-1.5 inches wide, and arranged oppositely along the stem. Leaves have short petioles (stalk of the leaf) and are sparingly pubescent (having tiny hairs) or lacking hairs beneath.
The stems lack hairs, often have a reddish tint when mature, become woody at the base, and are much-branched in the upper portions of the plant. These plants may be found growing as colonies due to a long horizontal rootstock that develops from an initial taproot. The fruit produced are long (5 inches or more), narrow follicles produced in pairs that turn reddish brown when mature. Flowers are small, white to greenish-white, and produced in terminal clusters.
Some identifying characteristics:
Stems and leaves secrete a milky sap when broken. Sprouts emerging from the underground horizontal rootstock may be confused with Common Milkweed (Asclepias syriaca) emerging shoots. However, the leaves of hemp dogbane are much smaller than those of common milkweed. When mature, these weeds may be distinguished by the branching in the upper portions of the plant that occurs in hemp dogbane, and also the smaller size of this weed compared to common milkweed.
For more information about how to control this weed watch the following video courtesy of AgPhD.
- Uva, Richard H., Joseph C. Neal, and Joseph M. DiTomaso. Weeds of the Northeast. Ithaca: Comstock Pub. Associates, 1997. Print.