How rare is the Mystic plant

[Flintsen]

I've had it drop 3 times in Meridia quests. I picked up 2 of them.

[Chette]

I see it drop about 50% of the time I'd estimate.
The problem I have is that when I run vale quests I usually farm them without picking up my end reward, so I don't have that many...guess I'll have to start recalling or teleporting back every time :(