Flat Sea Holly
- Name also: Flat Sea-holly, Blue Glitter Sea Holly, Blue Eryngo, Plains Eryngo
- Family: Carrot Family – Apiaceae (Umbelliferae)
- Growing form: Perennial herb.
- Height: 30–60 cm (12–25 in.). Stem solid, branched in upper part.
- Flower: Corolla regular (actinomorphic), bluish, less than 3 mm (0.12 in.) wide, petals 5, shorter than sepals. Sepals 5. Stamens 5. Pistil of 2 fused carpels, styles 2. Inflorescence dense, capitular umbel. Bracts large, almost the size of the inflorescence, lower ones narrow, with large-toothed–spiny margins, upper ones bluish, with entire or rarely serrate margins.
- Leaves: Alternate, base pod-like, basal leaves stalked, upper leaves stalkless. Blade of lower leaves elliptic–ovate, base heart-shaped, serrate, upper leaves lobed, with spiny margins.
- Fruit: Globose–egg-shaped 2-parted schizocarp with scales.
- Habitat: Ornamental plant, sometimes as an escape on dry, sandy and gravelly soil close to settlements.
- Flowering time: August–September.
Eryngiums are very rare in Finnish nature, but in general they are the largest genus of the umbellifers whose centre of biodiversity is in Mexico and South America. Only about twenty species grow in Europe, and most of these in the Mediterranean region. In Finland, eryngiums are sometimes grown as garden plants. The most commonly cultured plant is the sea holly, but even this is only rarely seen in our flower beds. More popular than the natural strain are various attractive cultivars with colourful flowers. Eryngiums are not only imposing perennials, but also suitable flowers for cutting and drying.
Flat sea holly is not a typical umbellifer, it rather resembles a cirsium: its stalkless umbels look more like capitular flowers than for instance the large compound umbels of the wild chervil. Insects are attracted to the flowers not only by the blue petals, but also by the subtending bracts, which are just as splendid as the petals. Flat sea holly attracts many kinds of hymenoptera, flies and butterflies as pollinators. The cultivars do not usually produce seeds, but the natural form sometimes seeds itself even outside of flower beds, and occasionally the species has been found as far North as in the Oulu region. Flat sea holly thrives best in dry and sunny spots: the hard structure and the smooth waxy surface of the shoot protect the plant from drying out even in strong sunshine. The light bluish-green colour of the sea holly, which stems from anthocyan pigments, protects the plant from the negative effects of overexposure to sun radiation as well. The poorer and drier the soil where the flat sea holly grows, the stronger the colour of the shoot.
Alpine Sea Holly
In the Eryngium genus there are quite many garden species that resemble flat sea holly, e.g. alpine sea holly (also known as alpine eryngo, queen of the alps) which comes from South European alps but can be found also in Finland in gardens and sometimes even outside.