Well, not really a thorn in my side, but more like prickers in my palm...splitting the poplar from the two trees I had that died along the back of our property and the trunk rounds have these "prickers" under the bark...and even some in the wood too. They are sharp, but not sharp like a raspberry thorn...is this common on poplar? (hybrid poplar to be specific...I planted these 25ish years ago for their fast 50-60' height)
Never seen that in any poplar I've had, that I remember. When I see that under bark, I think of birdseye figuring. Real common in maple.
Ive seen thorns like that inside logs. Apple is one that comes to mind. I've seen little thornlike bunps under tulip poplar bark.