A union with included bark usually will NOT have which of the following shapes?

A union with included bark typically forms a shape that allows for the bark to grow inward, creating a structure that can often appear as a circular or elliptical shape, where the bark on both sides of the union overlaps and has an inward projection. This inward growth of the bark can prevent proper fusion of the branches, leading to weak points in the structure.

When we consider the characteristics of each shape, a U shape is more indicative of a smooth, open, and free-growing union where there is no bark inclusion affecting how the branches align. This shape allows for good cambial contact and proper union development without the complications associated with included bark. In contrast, circular or elliptical shapes suggest a more constricted growth pattern, typical of branches with included bark. A square shape does not align with the growth patterns observed in trees with included bark either, but it is not as distinctly related to the nature of the included bark issue as the U shape is.

Choosing the U shape as the correct response reflects an understanding of how included bark can distort the growth pattern of tree unions, leading to shapes that appear circular or elliptical rather than open and flowing as a U shape would be.