Final answer:
Aquatic plants on another planet similar to Earth's would likely retain gametophyte dependency longer than terrestrial plants due to the ease of gamete transfer in water.
So, the correct answer is d) Gametophyte dependency.
Step-by-step explanation:
If we discovered another planet where plants had evolved similarly to those on Earth but had never left the water, one trait these plants might retain longer than plants on Earth is gametophyte dependency. On Earth, the evolution of plants included the development of certain adaptations to cope with life on land.
These adaptations include vascular tissue for transporting water and nutrients, leaves, roots, and protective features like waxy cuticles and a tough outer layer to protect spores. However, in an aquatic environment where plants are surrounded by water, these adaptations might be unnecessary or less pronounced.
For instance, the cuticle evolved to prevent water loss on land, an issue irrelevant in a fully aquatic environment. Without the selective pressures of terrestrial life, traits such as gametophyte dependency might be retained since water can readily facilitate the transfer of gametes for fertilization.
So, the correct answer is d) Gametophyte dependency.