Yes, SILVERWEED is a Scrabble word!

Letter values in Scrabble US: S 1, I 1, L 1, V 4, E 1, R 1, W 4, E 1, E 1, D 2.

Is it a valid word?

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

any of various twining shrubs of the genus Argyreia having silvery leaves and showy purple flowers
low-growing perennial having leaves silvery beneath; northern United States; Europe; Asia

Also: goose-tansy, goose grass, potentilla anserina.