Yes, PSYLLIUMS is a Scrabble word!

Letter values in Scrabble US: P 3, S 1, Y 4, L 1, L 1, I 1, U 1, M 3, S 1.

Is it a valid word?

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

plantain of Mediterranean regions whose seeds swell and become gelatinous when moist and are used as a mild laxative

Also: spanish psyllium, plantago psyllium.