Which floatingheart species is characterized by flowers that are densely covered with hair on the inner surface?

The species that is characterized by flowers with densely hairy inner surfaces is the crested floatingheart. This feature helps to identify it among aquatic plants. The hairy inner surfaces of the flowers may serve various purposes such as aiding in pollination by attracting pollinators or providing a surface for the adherence of pollen.

The little floatingheart, while also a member of the same family, does not possess this defining characteristic of hairy inner surfaces, making it less recognizable compared to the crested floatingheart. The water snowflake is known for its unique, snowflake-like flowers, but it does not exhibit the same hairy inner feature. Lastly, fanwort, primarily recognized for its submerged leaves and distinct growth patterns, lacks the specific floral trait associated with the crested floatingheart.

Thus, the presence of hair on the inner surface of the crested floatingheart's flowers distinguishes it from these other options, making it the correct choice in this context.