Yes, MADRONO is a Scrabble word!

Letter values in Scrabble US: M 3, A 1, D 2, R 1, O 1, N 1, O 1.

Is it a valid word?

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

evergreen tree of the Pacific coast of North America having glossy leathery leaves and orange-red edible berries; wood used for furniture and bark for tanning

Also: arbutus menziesii.