“Did you know that corn is a fruit?”
That single comment triggered some extensive research up here in the office at Severson Dells, as we collectively looked online and in books for definitions of what makes a fruit a fruit. It turns out that this is truly a much more complicated thing than any of us imagined (and yes, corn is technically a fruit).
My forestry school days were many years ago, and at that time I learned about such things as a “multiple of achenes,” but as a naturalist and environmental educator who works primarily with kids and the general public, I don’t throw around phrases like “multiple of achenes” without risking losing the attention of my audience. So, having not used botanical terms in their full glory for many years, I needed a refresher.
Let’s start off with a few botanical definitions so we are all on the same page.
Pistil: the female flower structure of a plant, the lower part of which is the ovary, which is hollow; inside the ovary, attached to its walls, are ovules, which, upon fertilization, become seeds.
Fruit: “a ripened ovary together with any appendages or dried flower parts that it still may retain” (William Harlow, Fruit Key and Twig Key to Trees and Shrubs). Harlow goes on to remind us that “the flower develops into the fruit, and the fertilized ovule becomes the seed.”
Vegetable: the root, leaf or stem of a plant that we eat (beet, lettuce, rhubarb, for instance).
So, now that we have that sorted out, let’s look at fruits, for not all fruits are created equal. To being with, a fruit can be either simple or compound. We’ll take a look at compound fruits first.
A compound fruit is what you have when a single fruit develops from multiple ovaries in either a single flower or multiple flowers.
You get an aggregate if you have one flower that has several ovaries that grow together as the fruit develops. An example of an aggregate fruit is a raspberry.
A multiple is what you get when several flowers, each with its own ovary, develop into small fruits, and those small fruits grow together into one big fruit. For this picture a pineapple.
A tomato is a simple fruit that grows from a compound ovary…so is it technically a compound fruit? I don’t know. Augh!
Next, we have plain old ordinary simple fruits: one pistil, one ovary. Simple fruits are classified as dry or fleshy, but sometimes the flesh is actually hard and firm, not what we would consider “fleshy” at all. Harlow goes on to explain that fleshy simple fruits are most likely (but not always) going to be a drupe, a berry or a pome, while the dry simple fruits are further divided based on whether or not they split along a seam when they dry out. If they split, they are dehiscent (such as legumes, follicles and capsules), and if they don’t split, they are indehiscent (achenes, samaras and nuts).
Let’s take a look at each.
First, the fleshy fruits.
Drupe: “a fleshy fruit in which the inner ovary wall is hard and bony, the outer one soft and fleshy” (Harlow). Drupes usually have one pit, although some have two. Drupes you may know include cherries, prunes, peaches, plums and almonds. (And I bet you thought the almond was a nut!)
Berry: “a fleshy fruit in which both inner and outer ovary walls are fleshy, and the seeds are distributed throughout” (Harlow). Berries include blueberries, huckleberries, gooseberries, tomatoes and persimmons, but they do NOT include strawberries, blackberries, raspberries or mulberries, which are all compound fruits known as aggregates (see above).
Pome: a fruit whose “outer wall is fleshy, the inner one papery, or like cartilage” (Harlow). Here we can consider the apple, pear, shadbush, mountain ash and hawthorn.
Now the dry, dehiscent fruits:
Legume: made from a simple pistil that when dry cracks open along two seams. You are probably quite familiar with legumes: beans, peas, clover, black locust, coffeetree.
Follicle: also from a simple pistil, but this fruit only cracks open along one seam when dry. Peonies and milkweeds are examples of plants that produce follicle fruits.
Capsule: this fruit develops from a compound pistil and can open up in a variety of ways. Some examples of capsules that you might know are the fruits of poppies, lilacs, catalpas and horsechestnuts.
And finally we have the dry, indehiscent fruits:
Achene: Harlow’s definition of an achene will likely leave you shaking your head: “a small, unwinged, but sometimes plumed, one-celled, one-seeded fruit.” Britannica.com’s definition is a little clearer: “dry, one-seeded fruit lacking special seams that split to release the seed.” A dandelion seed is a great example. If you are interested in a combo pack, the fruit if the sycamore tree is a multiple of achenes!
Samara: these dry seeds have papery “wings.” Picture the seeds that fall from maples or ashes.
Nut: from our friend William Harlow we understand a nut is “partially or wholly enclosed in a husk which may be papery, leafy, woody or spiny in character. The nut itself has a bony, or leather outwall and is usually one-seeded.” Whew! Britannica.com to the rescue: a “dry hard fruit that does not split open at maturity to release its single seed.”
Wow - who knew that the world of fruit could be so complicated!
Does Joe Q. Public care that fruits come in such an amazing variety? Probably not. But we nature nuts [“crazy,” 1846, from earlier be nutts upon “be very fond of” 1785), which is possibly from nuts (plural noun) “any source of pleasure” (1610s), from nut (q.v.). Sense influenced probably by metaphoric application of nut to “head” (1846, e.g. to be off one’s nut “be insane,” 1860] - from Online Etymology Dictionary, 2010, Douglas Harper), especially those with a botanical bent and a fondness for using accurate terminology, tend to find such detail quite exciting.
Go forth, my friends, and be fruitful in your discoveries!