Which plant form is characterized by an upright shape where the top and bottom are generally the same width?

The fastigiate form of a plant is characterized by an upright shape with branches or leaves that grow closely together, resulting in a profile that is often narrow from the base to the top. This growth pattern creates a tall and column-like structure, where both the top and the bottom are similar in width. The design is particularly useful in landscapes where verticality is desired, providing a clear and defined shape that can fit well in tight spaces, or be used to accentuate pathways and entry points.

In contrast, other forms exhibit different characteristics. The spreading form generally has a broader profile that extends outward, lacking the narrow upright characteristic of the fastigiate type. The weeping form features branches that droop downwards, creating a cascading effect rather than an upright silhouette. Irregular forms do not follow a consistent shape, leading to a more disorganized appearance that has no definitive width structure. Therefore, the distinct upright growth and uniform width at both the top and bottom define the fastigiate form as the correct answer.