Plantains, bananas and tropical bananas come from the same species of trees. The only thing that differentiates them is the size and sugar content of their fruits. Tropical bananas tend to be small and very sweet. They come in very large bunches.
The typical banana found in American grocery stores are called dessert bananas o the rest of the world and are medium sized in medium bunches and are still pretty sweet. Much is known about banana nutrition data such as that the banana fruit as an antioxidant rich fruit is good, but not as high as darker colored fruits which contain large amounts of pigment antioxidants.
Plantains are large and the bunches grow with less fruits on each than other varieties and the fruit is not sweet but not sour either. Plantains are hearty, have a high starch content compared to bananas (but lower compared to potatoes, rice and pastas) and are bland like a potato. Banana type trees bear fruit all year round.
Because of their low sugar content and the fact that they are picked still green, they can keep for a little while. These things have worked to make the plantain the 10th food staple of the world. They are high in many vitamins, minerals and carbohydrates. Plantains are often cooked and used like pasta and rice, while bananas and tropical bananas are often eaten raw and mixed into fruit salads, smoothies, and quick breads.