Yes, GUAYULE is a Scrabble word!

Letter values in Scrabble US: G 2, U 1, A 1, Y 4, U 1, L 1, E 1.

Is it a valid word?

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

much-branched subshrub with silvery leaves and small white flowers of Texas and northern Mexico; cultivated as a source of rubber

Also: parthenium argentatum.