Yes, PLANTAIN is a Scrabble word!

Letter values in Scrabble US: P 3, L 1, A 1, N 1, T 1, A 1, I 1, N 1.

Is it a valid word?

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

any of numerous plants of the genus Plantago; mostly small roadside or dooryard weeds with elliptic leaves and small spikes of very small flowers; seeds of some used medicinally
a banana tree bearing hanging clusters of edible angular greenish starchy fruits; tropics and subtropics
starchy banana-like fruit; eaten (always cooked) as a staple vegetable throughout the tropics

Also: plantain tree, musa paradisiaca.