Native to North America, Indian hemp (Apocynum cannabinum, Apocynaceae) can be found in open areas along water, forests, and disturbed areas throughout most of the continent. This plant bears a resemblance to the related milkweeds (Ascepias spp., Apocynaceae) but is notable in part for having branching stems and greater size. It blooms during the summer, producing dense clusters of tiny, white, bell-shaped flowers.
The shoots of Indian hemp are conspicuously red, contrasting with the large, green, oval leaves. It’s from these shoots that Indian hemp got its common name. Native Americans used the dried fibers for rope, snares, nets, baskets, and clothing. This plant is unrelated to cannabis plants (Cannabis spp., Cannabaceae) that produce what is commonly known as “hemp,” but the fibers can be used in the same manner.
As with milkweeds and most other members of the dogbane family (Apocynaceae), Indian hemp exudes a milky white sap when damaged. This fluid and all parts of the plant are highly toxic, containing cardiac glycosides and other compounds that can interfere with normal cardiovascular function.
This plant’s toxicity protects it from herbivory by most animals. Some insects like monarch butterfly larvae (Lepidoptera: Nymphalidae: Danaus plexippus) have developed a tolerance to the chemicals, allowing them to feed on these plants with little competition.