I've got a good photo of a flowering red plum, which did what you described, and needed removal. I cut it in half and photographed the inside. The bottom pedestle, in case you wonder about the crease...
Check out the included bark in the image, showing just how skinny the main leader was in the "pinched" area in-between.
Flowering plum are okay tree, unless loaded with weak defects in the nursery, or neglected. But they do commonly "push up" what you call antennae. |