Yes, JIMSONWEED is a Scrabble word!

Letter values in Scrabble US: J 8, I 1, M 3, S 1, O 1, N 1, W 4, E 1, E 1, D 2.

Is it a valid word?

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

intensely poisonous tall coarse annual tropical weed having rank-smelling foliage, large white or violet trumpet-shaped flowers and prickly fruits

Also: jimson weed, jamestown weed, common thorn apple, apple of peru, datura stramonium.