Remaining closed at maturity, as in 'indehiscent fruit'.
This is a botanical term. Dehiscence is when part of a plant splits open at maturity, for example a pod splitting open to release seeds. Last year in the garden, I learned that bitter melons are dehiscent: one day the fruit looked green and solid and ready to eat, and the next time I checked it looked like a half-peeled warty orange banana.
Indehiscent fruit does not split open and must expose its contents some other way - by decay, by being eaten, etc.
Etymology: early 1800s, from Latin dehiscere, to gape, open, or split.
Not to be confused with "indecent fruit", as indehiscent fruit is arguably quite demure. ;-)