Yes, HOSTAS is a Scrabble word!

Letter values in Scrabble US: H 4, O 1, S 1, T 1, A 1, S 1.

Is it a valid word?

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

robust east Asian clump-forming perennial herbs having racemose flowers: plantain lilies; sometimes placed in family Hostaceae

Also: genus hosta, genus funka.

Not playable in Scrabble US: FUNKA.