All plantains are not created equal

Most people are familiar with plantains: they are the larger, more homely cousins of the common banana. There are smaller, less well-known plants that are also called plantains, however. So what are the differences between the different "plantains?"

First, what characterizes the most popular form of plantain, the kind you see in the grocery store? Is it really just a bulked up banana? Both plantains and bananas are members of the family Musaceae, within the spectacular order Zingiberales, which also includes the bird of paradise, heliconia, canna lily, and ginger. These tropical plants are known for their bold colors and showy flowers. While they display a variety of forms, plants in Zingiberales can be identified by several common features: leaves with distinctive petioles harboring air canals, pinnately veined leaves with tears in between the secondary veins, making them appear pinnately compound, inferior ovaries, and leaf blades that are rolled into tubes within their buds.

Many people think that bananas grow on trees, but that is a misconception: the plants are actually gigantic perennial herbs. They are monocots, which do not have secondary growth and thus do not include "true" trees with woody tissue.

There are, however, plantains among the dicots. The catch is that these are plantains in name only, and are nothing like the banana-ish fruit that most people associate with that title. English plantains are members of the family Plantaginaceae, within the order Lamiales. Lamiales is a large order with many significant members, including olives, mints, bladderworts, and many others. The families in this order commonly have dry capsules as fruits, oppositely arranged leaves, gland-tipped hairs, and store carbs in the form of oligosaccharides. The family Plantiginaceae is unique within the order because it has 2-locular anthers with U or V shaped slits. Its fruits are dry capsules, distinctly different from the berries produced by the Musaceae plantains (yes, bananas and plantains are berries!).

The English plantains are diminutive herbs, fairly unexciting compared to the large leafy pseudo-trees of the Musaceae, and it has become an invasive threat to biodiversity after being introduced to the Americas from Britain.

There is one other "plantain," the water plantain, a member of the Alistmataceae, in the order Alismatales. These are aquatic herbs, with creeping rhizomes and laticifers, which produce a milky sap. Being monocots, they are actually more closely related to the berry plantains than they are to the dicot English plantains, even though their herbaceous forms are more similar to the Plantaginaceae than the Musaceae.

Earlier we looked at remarkable convergence of body forms among cactuses and euphorbs, but this case of mistaken identity is much different. Here, the multiple "plantains" are not the result of convergent evolution, they are all extremely unique and lack even superficial similarities in their morphology. In this case, it is our terminology that can cause confusion, with the same name being applied to unrelated species. Considering how much tastier the classic Musaceae plantain is than the scrappy little English plantain and the marsh-dwelling water plantain, it's important to know the distinctions!

(Image credits: plantains, banana "tree", and English plantain and water plantain.)