This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Herbs with prickly foliage and bracts. Leaves lobed or dissected or undivided, with rigid teeth. Flowers sessile, in dense heads or spikes surrounded by a whorl of bracts. About 100 species, from the temperate and warmer regions, absent only from South Africa. Two or three species are cultivated on account of the bright blue colour of the involucral bracts, which are of long duration. The name is of classical origin,but its application is uncertain. The Sea Holly, E.marit-imum, belongs to this genus.
1. E. alpinum. - A dwarf perennial about 18 inches or 2 feet high. Radical leaves on long petioles, undivided, deeply-cordate; cauline sessile, 3- or 5-lobed, with sharp teeth. Involucre multifid, with spinose teeth, ultimately assuming a deep blue tint. Flower-head oblong. Switzerland.
2. E. Bourgati. - Similar to the last, but with the radical leaves triternately deeply divided, lobes terminating in long slender sharp teeth, and the flower-head globose. A very pretty glaucous green species, the involucres and stems at length blue. It comes from the South of France.
3. E. amethystinum. - About 3 feet high. Leaves about a foot long, bipinatifid; segments few, long, and narrow, with spinose teeth. A more branching plant than either of the foregoing. Involucres and upper branches blue. A native of the Tyrol, etc.