SIMPLE DRY FRUITS
Simple dry fruits are those in which the fruit wall -- the skin, rind, or husk -- is leathery, papery, or woody. Among the most important simple dry fruits are the following:
Follicles are primitive fruits developing from ovaries divided into only one carpel, and splitting along one side , where their seeds escape. (Remember that carpels are the wedge-shaped chambers you see when you cut across a tomato.) In our backyards we might see follicles on our ornamental peonies, larkspurs, and columbines, as well as the weedy milkweed, and the sandvine pictured here. Notice how the sandvine's follicle splits along just one side. The white fuzz in the picture consists of the "parachutes" atop small, dark seeds. The "parachutes" carry the seeds on wind currents. The two orange spots on the fruit are just a couple of beetles mugging for the camera!
Legumes also develop from one-carpel ovaries, but they split along two sides, not one, as in the case of follicles. The bean family, one of the most commonly encountered plant families backyard naturalists are likely to meet, produces legume-type fruits, so we can see this fruit type on weeds such as clover and alfalfa, the various kinds of garden beans and peas, and trees such as locust and redbud. The picture above shows the legume fruit of the Garden Pea, Pisum sativum, from my own garden. I've removed one side of the pod so you can see the peas neatly arranged inside. Now you know where peas come from! Something cool about this picture is that at the far right you can see the flower's calyx, and at the far left you see the shriveled remains of the pistil's style and stigma, so that it's easy to believe that the pea pod really developed from the flower's ovary.
Capsules, such as that of the Jimson Weed pictured at the right, develop from ovaries composed of more than one carpel. Capsules split in various ways, or don't split at all. In our backyards, ornamental poppies produce capsules, as do horsechestnut trees. By the way, in our Jimson Weed picture, this is a good example of a plant doing what it can to protect its seeds. Not only are Jimsonweed capsules well protected with spines, but also the seeds are quite poisonous, and have been known to kill people! The Jimsonweed's capsule shown here is about the size of a golf ball.
Achenes are small fruits containing single seeds which nearly fill the fruit cavity. The seed coat doesn't stick to the "fruit wall." In our backyards, achenes are the fruit-type of the huge composite family, which includes sunflowers, daisies, dandelions, dahlias, zinnias, coreopsises. Buttercups, in the buttercup family, shown at the right, also produce achenes. In the picture "A" at the top of course is the buttercup flower showing five petals, many stamens, and in the flower's center there are many separate pistils. "B" shows a flower after it has been pollinated. All but one of the yellow petals have fallen off, just a few stamens remain, and the pistils are growing . "C" shows a head of achenes. Later the achenes will drop off independently. If the achenes stuck together to form a berry-like fruit, the fruit would be considered an "aggregate fruit," considered on another page. At the left is one of the best-known examples of the achene-type fruit. It's the fruiting head of a Dandelion. You can barely see inside the fluffy head dozens of brownish achenes. Atop each achene is a white "parachute" that carries the achene away when you or the wind blow on it.
Grains are like achenes, except that their seed coats are fused with the "fruit wall," so that seeds and fruit are merged into a single unit. I don't expect that to really sink in for most of you because it's a pretty nit-picking definition. One way to fix what a grain is to remember what you see in the photo at the right. These are grains of popcorn exactly as I took them from a store-bought bag of popcorn, except that I've cut the top grain down the middle so you can see the embryo inside it. If I'd plant these grains instead of pop them, that embryo would eventually send a rootlet out the bottom of the grain, and a sprout out of the top, and a new corn plant would develop. Grains are produced by the huge grass family, so they are abundantly represented in our backyards. However, most grass-family grains are so tiny that you'd a lot of magnification to see the embryos inside them.
Samaras are similar to the above two fruit types, except that they are equipped with "wings," which help them travel by wind. In our neighborhoods, samaras appear on trees such as maple and ash. The samaras pictured here are those of Boxelder, a common street tree of eastern North America, a member of the maple family. You can see that each of the four pictured samaras has a bulging, roundish area at the base, which is the seed, and then a long, flat, veiny wing. Since samaras have only one wing, when they are torn away by the wind, instead of sailing like a plane, they spin in the air, round and round. Because of the spinning, some kids call them "helicopters."
Nuts are non-splitting, hard and bony fruits containing only one seed. Neighborhood examples include oaks, walnuts, hickories, chestnuts, and hazelnuts. When nuts occur on oak trees, they have a special form and are known as acorns. At the right you see acorns from a Water Oak (Quercus nigra) near my home. Notice the scaly cups in which each nut is seated. This is typical of all acorns. In some oak species the cup nearly covers the nut, in others it covers only a little. Often nuts fall from their cups leaving the cups empty on the twig, but eventually the cups themselves fall to the ground.