Yes, AGERATUM is a Scrabble word!

Letter values in Scrabble US: A 1, G 2, E 1, R 1, A 1, T 1, U 1, M 3.

Is it a valid word?

AGERATUM is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

rhizomatous plant of central and southeastern United States and West Indies having large showy heads of clear blue flowers; sometimes placed in genus Eupatorium
any plant of the genus Ageratum having opposite leaves and small heads of blue or white flowers

Also: mist-flower, conoclinium coelestinum, eupatorium coelestinum.

Not playable in Scrabble US: MISTFLOWER.