Petals are pink, purple, or white and turn straw colored at maturity?

• A. Diffuse Knapweed
• B. Leafy Spurge
• C. Russian Knapweed
• D. Spotted Knapweed

Answer: (C)

Understanding how flower color changes as a head matures helps distinguish these knapweeds. The description—petals that start pink, purple, or white and fade to a straw color as they reach maturity—fits Russian knapweed. Its florets begin with pink-to-purple hues and gradually pale to a straw or tan color as seeds develop, which is a characteristic identifying trait.

Other options don’t fit as cleanly. Leafy spurge is not a knapweed at all and shows yellow-green bracts instead of pink/purple petals. Diffuse and spotted knapweed typically keep their pink-to-purple tones longer and have other distinguishing features (such as spots or bract patterns) rather than fading to a straw color at maturity.