Spotted & hybrid knapweed
(Centaurea stoebe & Centaurea x psammogena = C. stoebe x C. diffusa)
Spotted & hybrid knapweed (Centaurea stoebe & Centaurea x psammogena = C. stoebe x C. diffusa) is a non-native, short-lived perennial forb that reproduces mainly by seed. Spotted knapweed can grow up to 900 seeds per plant annually that are viable for up to 8 years. The key to distinguishing spotted from other knapweeds is the black-tipped, spiny, involucral bracts (phyllaries) at the base of the flower. Unlike diffuse knapweed, it does not have a long, distinct terminal spine at the tip of the bracts. Spotted & hybrid knapweed can grow up to 3 feet tall on rigid stems that are openly branched on the upper half of the plant. Urn-shaped flowers are solitary on the tip of each branch. Flowers are pink to purple and rarely white. Leaves on the stem are alternate, deeply lobed, and become smaller and simple near the tips of the stem. Basal rosette leaves are deeply lobed and up to 6 inches long. Flowers bloom from June to October and seed-set usually occurs by mid-August. Spotted knapweed can also reproduce vegetatively from lateral roots. Spotted knapweed can cross with diffuse knapweed to form the hybrid knapweed.