Genus: Sea holly Eryngium Photo/Illustration: Michelle Gervais Sea holly (Eryngium) air-ING-ee-um Apiaceae Plants in the genus Eryngium are characterized by spiny basal rosettes with conspicuous white veins. Rounded nubs of thistle-like flowers are borne on branched stems. Noteworthy characteristics: Wonderfully sculptural accents with icy blue to ghostly silver toothed bracts and flower heads, which persist for a long time. Care: Depends on species, either dry or wet soil, in full sun. Propagation: Sow seed in containers when ripe, divide plants in spring (plants are slow to recover). Problems: Root rot, slugs, snails and powdery mildew. Eryngium View the discussion thread.