Yes, BITTERROOT is a Scrabble word!

Letter values in Scrabble US: B 3, I 1, T 1, T 1, E 1, R 1, R 1, O 1, O 1, T 1.

Is it a valid word?

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

showy succulent ground-hugging plant of Rocky Mountains regions having deep to pale pink flowers and fleshy farinaceous roots; the Montana state flower

Also: lewisia rediviva.