I tend to agree with Tom, however .............
It could be a stress crack that formed in the plank. If the crack closes easily when clamped (no appreciable resistance) the stresses could have been relieved when the stock blank was cut out. If that is the case, and it is properly glued up, it would likely be a permanent repair. I would glue it up, closely examine the repair and, considering the overall quality of the blank, decide from there. If there is appreciable resistance, I would definitely not use it.
I am a firm believer in yellow wood glue such as Titebond II. I have used gallons of it in cabinetmaking and, in my experience, the adjacent wood will fail before a properly done glue joint. You do have to get good glue coverage throughout the crack. There was a recent thread on crack repair that addressed types of glue and methods of application.
Laurie