Yes, COTTONWEED is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, T 1, T 1, O 1, N 1, W 4, E 1, E 1, D 2.

Is it a valid word?

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

an American everlasting having foliage with soft wooly hairs and corymbose heads with pearly white bracts
any of various plants of the genus Froelichia found in sandy soils and on rocky slopes in warmer regions of America; grown for their spikes of woolly white flowers

Also: pearly everlasting, anaphalis margaritacea.