14. (15 points) Eight $2 \times 1$ small rectangles as shown in the figure can be used to form a $4 \times 4$ square. If a square formed by these rectangles is the same as another square after rotation, they are considered the same square. How many different square patterns can be formed that have only one diagonal as a line of symmetry?
【Analysis】For convenience in drawing, use the diagram
$\qquad$ to replace the $2 \times 1$ rectangle in the problem, and solve by drawing based on the properties of symmetry.

【Solution】Solution: Use the diagram $\square$ $\because$ $\qquad$ to replace the $2 \times 1$ rectangle in the problem. Since one diagonal, when rotated 90 degrees, coincides with the other diagonal, we only need to consider the case where the diagonal passing through the top-left vertex is the axis of symmetry. In this case, the number of stars on the diagonal of the square formed must be even, and the $2 \times 2$ small square in the top-left corner can only be one of the shapes in Figure $A$ and Figure $B$, while the $2 \times 2$ small square in the bottom-right corner can only be one of the shapes in Figure $A$ and Figure $C$.
(1) First, consider the case where the $2 \times 2$ small squares in the top-left and bottom-right corners are one of the two shapes in Figure $A$.
In this case, the $2 \times 2$ small square in the top-right corner has two stars. Since the other diagonal cannot be the axis of symmetry, the $2 \times 2$ small square in the top-right corner cannot be any of the shapes in Figure $A$, but must be one of the shapes in Figure $D$. Excluding the cases of rotational coincidence, there are only the following 8 possibilities:
(2) When the $2 \times 2$ small square in the top-left corner is one of the two shapes in Figure $B$ and the $2 \times 2$ small square in the bottom-right corner is one of the two shapes in Figure $C$,

it is impossible to form a shape that is symmetrical only about the diagonal passing through the top-left vertex.
Answer: There are 8 ways to form a square that is symmetrical only about one diagonal.