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.
A closely allied North American genus or sub-genus with a campanulate perianth whose tube is three or four times as long-as the segments of the limb. H. hyacinthinum has fleshy herbaceous narrow leaves about a foot long, and flowers in umbels at the summit of a scape. Flowers blue or white, 10 to 30 in an umbel; umbel with an involucre of numerous small bracts.