Which of the following is considered a prohibited plant?

The correct answer is associated with the genus Erythroxylon, which includes plants like the coca plant that are used to produce cocaine. These plants are classified as prohibited due to their association with illegal drug production and trafficking. This classification is rooted in legal frameworks designed to control substances that pose risks to public health and safety.

In contrast, other options present common plants that do not have such legal restrictions. Cannabis, although often debated in legal contexts, is not uniformly prohibited; its status can vary by jurisdiction, especially where laws have been amended to allow for its cultivation under specific conditions. The category of common ornamental plants and legal agricultural plants does not encompass any elements that would align with the definition of prohibited plants under laws concerning drug enforcement or other regulatory frameworks.