The flowerheads have a dark-coloured elevated disk.
speciosa, I to 2 ft., is a showy composite, of easy culture in good garden soil; it produces large corymbs of flowerheads, with numerous narrow blue ray-florets surrounding the yellow disk.
The flowerheads of greater knapweed have long rays which are lacking in common knapweed.
They have profuse, fragrant, bright golden yellow, spherical, fluffy flowerheads, 5mm (0.25in) across.
The active compounds hypericin and hyperforin are concentrated in the flowering heads of the plant,and can be accessed in teas made from the flowerheads, capsules containing dried flowers or liquid alcohol extracts.