Botany for Gardeners - The Basics of Fruits
Calling all fruits and nuts!
Once a flower has been pollinated successfully, the outcome is going to be a structure that contains seeds. As with flowers, these structures come in a mind-bending variety of sizes, shapes and compositions. They range from very simple one-seeded affairs to very complex constructs with hundreds, or even thousands, of seeds within. These amazing seed containers are known as fruits.
In botany, the term "fruit" does not mean something you cut up and put on your breakfast cereal, but rather the structure that bears the seeds of the plant. As such, many plant parts we know of as vegetables are actually fruits. A few very familiar examples are tomatoes, eggplant and squash. Botanically, these are all fruits. Even a sugar pea pod is technically a fruit.
Will you have yours dry or moist?
Fruits divide into two basic categories, the dry fruits and the fleshy fruits. Each type has terminology peculiar to it, used to describe the various types and anatomical parts. For purposes of this article, I want to introduce you to the terminology describing the fruits most familiar to you. But first I need to introduce a term that is common to all fruiting structures on flowering plants, and that is the term carpel. This is the term used to describe a simple ovary, or one unit of a compound ovary. An example of a fruit with a single carpel is a pea pod. The pod with peas within is a single chamber with several ovules (when immature) or seeds (when mature). This single chamber is a carpel, and this is true whether there is one seed or ten seeds within it. Put three carpels together and you have a three-chambered capsule (see akee fruit at left). Fruits like this are found on cotton and other mallows like Hibiscus.
Now that you know what a carpel is, let's return to the two categories of fruits and start with the dry fruits. We have two terms to describe them: dehiscent and indehiscent. Dehiscent fruits are those that open up naturally to release or reveal the seeds, such as some of the legumes with pods that split in half when mature. Those that are indehiscent do not open at maturity. Examples of familiar indehiscent fruits are the black walnut, Juglans nigra and the pecan, Carya illinoinensis. Terms to describe different kinds of dry fruits are numerous, but a few for familiar fruits are the samara, exemplified by the fruit of the maple, the achene, as demonstrated by the sunflower fruit, and the grain or caryopsis, well-known in grasses.
Juicy enough to eat!
Next let's look at the fleshy fruits, which are even more familiar to gardeners. Almost all fleshy fruits are indehiscent but they are quite varied in their structures and in the terminology used to describe them. Here I'll introduce you to the terms for fruits we all know and love. What do the peach, coconut, mango and olive have in common, besides the single seed? They are all drupes, a fruit formed from a single carpel, with an outer fleshy layer called the pericarp and an inner, hard layer known as the endocarp. This is easier to remember if you think of it as an outer layer, or perimeter of the carpel, that is fleshy, and an inner or endo layer of the carpel. How about the guava, tomato and blueberry? They are all berries, one or more carpels formed within a thin covering, very fleshy within, with seeds embedded in the fleshy part. However, a strawberry is not a berry, but an aggregate, with what looks like the seeds on the outside being the actual fruits (achenes) and the red fleshy part being a receptacle upon which the fruits form.
OK, now, a mulberry has to be a berry, right? Nope, that one is a multiple, a fruit formed from many flowers clustered closely together. If you take the time to look closely at a mulberry, you can see it composed of actual individual little fruits, each with a dried pistil tip. Apples are known as pomes, the fleshy part being formed from the receptacle surrounding the carpels (the inedible core parts), while watermelon is a pepo, which is berry-like. For me, the most fun fruit term is the hesperidium. Have you ever seen one of these? If you've ever peeled an orange, grapefruit or tangerine, you've disassembled the hesperidium!
(Editor's Note: This article was originally published on July 23, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
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