Yes, TRILLIUM is a Scrabble word!

Letter values in Scrabble US: T 1, R 1, I 1, L 1, L 1, I 1, U 1, M 3.

Is it a valid word?

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

any liliaceous plant of the genus Trillium having a whorl of three leaves at the top of the stem with a single three-petaled flower

Also: wood lily, wake-robin.