CAT;
Because of the single stalk, I'd say it's a Sinularia rather than a Lobophytum but other than to eliminate a few Sinularia such as S. elegans (Yellow Fiji-duh, that's a no brainer

), S. notand (one of the leathers confused with "colt" corals) , S. brassica, and S. flexibillis-LOL, I love that name-(Rasta Leather) it's really hard to narrow it down to a species level. Maybe someone else here can give a more positive ID. Most all leathers show fast growth and very easy to frag.
And that one's cool looking!
Alice