Which of the following is an example of ephemeral annual xerophytes?

Ephemeral annual xerophytes are plants that have adapted to survive in arid environments by completing their life cycle quickly, particularly in response to infrequent rainfall. They often germinate, grow, flower, and produce seeds within a short time frame, typically during periods of moisture.

Argemone mexicana is a prime example of such a plant. It is a species of flowering plant that can thrive under drought conditions and often exhibits rapid growth after rainfall, which is characteristic of ephemeral annuals. This ability allows it to effectively exploit temporary water availability, enabling it to flourish in the harsh environments typical of xerophytic conditions.

In contrast, Opuntia (a type of cactus) is more perennial in its growth form, while Azolla and Pistia are both aquatic plants and do not exhibit the xerophytic adaptations associated with surviving in arid environments. Thus, Argemone mexicana stands out as the correct answer due to its specific adaptations to ephemeral growth in dry conditions.