Yes, PERIANTHS is a Scrabble word!

Letter values in Scrabble US: P 3, E 1, R 1, I 1, A 1, N 1, T 1, H 4, S 1.

Is it a valid word?

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

collective term for the outer parts of a flower consisting of the calyx and corolla and enclosing the stamens and pistils

Also: floral envelope.

Not playable in Scrabble US: PERIGONE, PERIGONIUM.