AGERATUM
ageratum
(noun) any plant of the genus Ageratum having opposite leaves and small heads of blue or white flowers
mistflower, mist-flower, ageratum, Conoclinium coelestinum, Eupatorium coelestinum
(noun) rhizomatous plant of central and southeastern United States and West Indies having large showy heads of clear blue flowers; sometimes placed in genus Eupatorium
Source: WordNet® 3.1
Etymology
From the genus name.
Noun
ageratum (usually uncountable, plural ageratums)
Any of the genus Ageratum of tropical American herbs, annuals and perennials, from the sunflower family Asteraceae, tribe Eupatorieae; they are sometimes used in floral displays.
Source: Wiktionary
A*ger"a*tum, n. Etym: [NL., fr. Gr. (Bot.)
Definition: A genus of plants, one species of which (A. Mexicanum) has
lavender-blue flowers in dense clusters.
Source: Webster’s Unabridged Dictionary 1913 Edition