Yes, THYRSES is a Scrabble word!

Letter values in Scrabble US: T 1, H 4, Y 4, R 1, S 1, E 1, S 1.

Is it a valid word?

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

a dense flower cluster (as of the lilac or horse chestnut) in which the main axis is racemose and the branches are cymose