| From midsummer to early autumn, Eryngium planum bears many rounded umbels, 1/2 to 3/4 inch long, of light blue flowers with spiky, blue-green bracts, to 1 inch long. The basal leaves on this clump-forming, evergreen perennial are toothed, egg-shaped, dark green, 2 to 4 inches long, and the stem leaves are spiny and blue-tinted, with heart-shaped bases. If the flowers are cut before they are fully open, they can be used for arrangements. 'Silverstone' produces thistle-like umbels of white flowers. |