General Description: Black knapweed is a perennial growing from 1 to 5 feet (20 to 150 cm.) tall. Stems are upright and branched and typically covered in short hairs. It flowers from summer to fall.
Flower Description: Flowerheads occur at branch tips. Bracts at base of flowerhead covered with dark brown or black fringed margins up to 3 times as long as the bract. Flowerheads made up of 40 to 100+ purple (or rarely white) flowers.
Leaf Description: Basal leaves have leaf stalks and are narrow with widest point near the base of the leaf or with the widest point at the middle. The stem leaves become smaller and narrower moving up the stem and stalkless. Leaf margins slightly toothed or smooth.
Stem Description: Black knapweed has one to many branching stems covered in hairs.