This section is from the "The Herb Hunters Guide" book, by A. F. Sievers. Also available from Amazon: Herb Hunters Guide.

Figure 62.Hemp dogbane (Apocynum cannabinum)
Black hemp, black Indian hemp, Canadian hemp, American hemp, amy-root, bowmans root, bitterroot, Indian-physic, rheumatism weed, milkweed, wild cotton, Choctaw-root.
Hemp dogbane is a native of this country and may be found in thickets and along the borders of odd fields throughout the United States.
Hemp dogbane is from 2 to 4 feet high, with erect branches and sharp-pointed, short-stalked leaves from 2 to 6 inches long. The small greenish white flowers which appear from June to August are borne in dense heads followed later by the slender, pointed pods which are about 4 inches in length. The plant contains a milky juice.
The roots of a closely related species, Apocynum androsaemifolium L., are also collected. The branches of this plant are diverging and forked and the flower heads loose and spreading. It also contains a milky juice. There are several well-recognized forms which formerly were recognized as varieties of A. cannabinum and A. androsaemifolium, but which are now considered distinct species. The roots of all these species possess somewhat similar properties, but they are not all acceptable to the trade.
The root, collected in autumn.
 
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