Eastern Forest Threat Center - Spotted Knapweed

Spotted knapweed is a biennial or short-lived perennial. Plants typically form a basal rosette of leaves in the first year and flowers in subsequent years. The rosette leaves are approximately 8 in. long by 2 in. wide and borne on short stalks. Flowering stems are erect, 8 to 50 in. tall, branched above the middle, and sparsely to densely hairy. Unstalked stem leaves are alternate, with leaf size decreasing towards the tip of the stem. Flowers, appearing from June to October, are purple to pink with 25 to 35 flowers per head. Flower heads usually remain on the plant. Spotted knapweed reproduces primarily by seed. It is most common in sunny habitats with well-drained or gravelly soils and grows on heavily disturbed sites, roadsides, agricultural field margins, undisturbed dry prairies, oak and pine barrens, rangeland, lake dunes, and sandy ridges. It releases a toxin into the soil that hinders or prevents the growth of neighboring species, which reduces plant diversity and limits forage and crop production. Water holding capacity of soil decreases as spotted knapweed taproots replace the network of native plant root systems, often increasing surface runoff and sedimentation.

Visit Web Source for this description...