Submitted by: Erin, USA
The Short Answer: There are really two questions here. Let’s deal with the easy one first. There are two ideas of what qualifies as a fruit. The culinary definition says any generally sweet plant parts are fruits. This includes all the things we typically think of as fruit, such as apples, pears, and berries of many kinds. It also usually includes things like rhubarb. And it definitely includes bananas.
To a botanist a fruit is “… any ovary and its accessory parts that has developed and matured. It also usually contains seeds.” (From Introduction to Plant Biology, by Kingsley R. Stern) The ovary of a plant is part of the flower pistil. Most pistils are shaped like a vase, with a rounded bulb and a thin neck. The ovary would be the bulb. Once the pistil is fertilized with pollen, the seeds develop in the ovary and the ovary often becomes large and fleshy, like an apple or a peach. The botanist’s definition of fruit includes most of the things we usually think of as fruit, such as apples, peaches and berries. It would not include rhubarb, which is a plant stem and does not come from the ovary. It would also include some things people don’t typically think of as fruit, such as tomatoes, green beans, and avocados.
The botanist’s definition would most definitely include bananas, which are the developed ovaries of the banana plant. So by any definition I’m aware of, a banana is a fruit.
Is a banana tree an herb? Here’s where I think your doctor’s confusion comes from. The culinary definition of an herb is basically any plant part that has a distinctive odor or taste useful in cooking. I’m not sure a banana qualifies for that definition. Botanists however, split plants into two major groups, herbs and trees. Trees have a woody interior that persists year after year and supports the plant. Wood is the interior structure of mostly dead cells that strengthens the tree, allowing it to grow tall and survive multiple years. Trees can be as huge as redwoods or as small as the dwarf willow (Salix herbacea), which only grows to be about six cm tall (2 in.). Many botanists would limit the use of “tree” to plants that grow much larger (as hinted at by the dwarf willow’s Latin name “herbacea” which suggests that it’s like an herb).
Herbs include almost everything that isn’t considered to be a tree. It’s important to note that this is a descriptive term, not a taxonomic or evolutionary category. A spruce tree and a willow tree are clearly both woody trees, but they are not at all closely related. The willow is an angiosperm, a flowering plant, whereas the spruce is a gymnosperm. Most herbs are angiosperms, much more like the willow tree than they are like a spruce.
Banana trees grow from an underground root system called a corm, which can last for many years. Each corm sends up one or more shoots, which develop large leaves. The thick stalks of these leaves wrap around each other and thicken into the trunk of the banana “tree.” A central stem comes up through the leaf stalks and develops the banana “heart,” which is a structure that includes multiple small flowers, each of which has an ovary that develops into a banana. Once the bananas have ripened, the entire plant dies back to the ground, and the corm sends up a new shoot. Even though a banana plant can get to be over 7.5 meters tall (25 feet), it only lasts about a year or so. And the interior of it is not a structure of dead cells as with wood. So a banana “tree” is not technically a woody tree.
Therefore, to a botanist, banana is an herb. Your doctor is right about that. But from a botanist’s standpoint, whether something is an herb or not is about the plant, not the fruit. Many, if not most, herbs have fruit, including the banana tree.
If a banana is a fruit, where are the seeds? Ah, interesting question. Bananas and plantains come from plants in the genus Musa, which is native to Southeast Asia. The commercially grown banana is a hybrid of at least two species, Musa acuminata and Musa balbisiana. As with many hybrids, when M. acuminate and M. balbisiana combine, the pairing of chromosomes often goes awry, with the resulting hybrid offspring ending up with three sets of chromosomes, instead of the usual two. As is also often the case, the “triploid” hybrid is almost entirely sterile. Seeds rarely form. Which is nice for those of us who love the banana fruit. The picture here shows what a wild banana looks like and as you can see, it is full of fairly large seeds, which would spoil the fun of a banana split, I’m afraid.
So even if you don’t care whether a banana tree is a true tree or really just a large herb, you should be glad it is a sweetly defective fruit.
Hippolyte, I, Jenny, C, Gardes, L, et al. (2012). Foundation characteristics of edible musa triploids revealed from allelic distribution of ssr markers. Annals of botany, 109(5), 937-51.
Stern KR, Jansky S, Bidlack, J. (2003). Introductory Plant Biology. McGraw-Hill Higher Education. New York.