Yes, BITTERWEED is a Scrabble word!

Letter values in Scrabble US: B 3, I 1, T 1, T 1, E 1, R 1, W 4, E 1, E 1, D 2.

Is it a valid word?

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

widespread European weed with spiny tongue-shaped leaves and yellow flowers; naturalized in United States
any of numerous chiefly North American weedy plants constituting the genus Ambrosia that produce highly allergenic pollen responsible for much hay fever and asthma

Also: bristly oxtongue, picris echioides.