Yes, cacti is a Scrabble word!
...and is worth 9 points in Scrabble, and 11 points in Words with Friends
cacti
Noun
1. Any succulent plant of the family Cactaceae native chiefly to arid regions of the New World and usually having spines
What Scrabble words can I make with the letters in cacti?
3 Letter Words
2 Letter Words