Apocynum cannabinum - Dogbane

From WikipediaApocynum cannabinum (Dogbane, Amy Root, Hemp Dogbane, Prairie Dogbane, Indian Hemp, Rheumatism Root, or Wild Cotton) is a perennial herbaceous plant that grows throughout much of North America - in the southern half of Canada and throughout the United States. It is a poisonous plant: Apocynum means "poisonous to dogs". All parts of the plant are poisonous and can cause cardiac arrest if ingested. The cannabinum in the scientific name and the common names Hemp Dogbane and Indian Hemp refer to its similarity to Cannabis as a fiber plant (see Hemp), rather than as a source of a psychoactive drug.

Although dogbane is poisonous to livestock, it likely got its name from its resemblance to a European species of the same name. 

In the fall, when toxins drain to the roots, the plant can be harvested for fiber, which can be used to make strong string and cordage for use in bows, fire-bows, nets and tie-downs.