This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Eupatorium coelestinum L. Sp. Pl. 838. 1753. Conoclinium coelestinum DC. Prodr. 5: 135. 1836.
Pubescent or puberulent, branched, 1°-3° high. Leaves opposite, petioled, ovate, obtuse or acute at the apex, truncate at the base, or abruptly contracted into the petiole, crenate-dentate, 1 1/2'-3' long, 9-18" wide; inflorescence cymose-corymbose, rather compact; heads 2"-3" high; involucre broadly campanulate, its bracts linear-lanceolate, acuminate, equal or nearly so, in 1 or 2 series; receptacle conic; flowers blue or violet.
In moist soil, New Jersey to Florida, Illinois, Michigan, Kansas, Arkansas and Texas. Also in Cuba. Aug.-Oct.