What is "polemonium caeruleum"

Valerian \Va*le"ri*an\, n. [LL. valeriana, perhaps from some person named Valerius, or fr. L. valere to be strong. powerful, on account of its medicinal virtues: cf. F. val['e]riane.] (Bot.) Any plant of the genus Valeriana. The root of the officinal valerian ( Valeriana officinalis) has a strong smell, and is much used in medicine as an antispasmodic.

Greek valerian (Bot.), a plant ( Polemonium c[ae]ruleum) with blue or white flowers, and leaves resembling those of the officinal valerian.

Polemonium caeruleum, known as Jacob's-ladder or Greek valerian, is a hardy perennial flowering plant. The plant produces cup-shaped, lavender-coloured or white flowers. It is native to temperate regions of Europe.