22 Mar 2012

Osage Oranges Were Made For Megafauna

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Since arriving in Virginia, Karen and I have frequently marveled at the Osage orange, a fruit-producing tree not encountered in my native Pennsylvania or in New England where we attended college and resided for decades.

The Osage orange was evidently ill-advisedly imported into Virginia as a decorative tree, and it responds to that hospitality by covering the ground every Fall with enormous bumpy fruits that nothing eats and which simply lie on the ground and rot.

I wondered out loud recently why a tree would bother to produce enormous fruits in great quantity that were inedible. Fruit production, after all, constitutes a system of bribery by members of the botanical kingdom. The tree or bush produces a tasty fruit or berry, and birds and animals consume them and consequently carry away and redistribute the plant’s seeds.

There are all those Osage orange trees busily producing gigantic, but inedible, citrus fruits that nobody wants. Why is this? I wondered. It just seemed very strange.

Happily, Karen found the answer just a few days later, in American Forests.

It turns out the Osage orange fruits, like certain others, used to have customers who liked eating them. Unfortunately, their natural Pleistocene megafauna audience went extinct.

[L]et’s return to the forlorn fruit of the Osage orange. Nothing today eats it. Once it drops from the tree, all of them on a given tree practically in unison, the only way it moves is to roll downhill or float in flood waters. Why would you evolve such an over-engineered, energetically expensive fruit if gravity and water are your only dispersers, and you like to grow on higher ground? You wouldn’t. Unless you expected it to be eaten by mammoths or ground-sloths.

According to my field guide, Osage-orange has a limited natural range in the Red River region of east-central Texas, southeastern Oklahoma, and adjacent Arkansas. Indians used to travel hundreds of miles for the wood, prized as the finest for making bows. Then European settlers planted it widely as living fences, taking advantage of the tree’s ability to spread via shoots from lateral roots. But Osage-orange persisted, and became widely naturalized long after the invention of barbed wire rendered them useless to farmers. The tree can now be found in 39 states and Ontario. If Osage-orange does so well elsewhere, why was it restricted to such a small area?

The answer likely lies in the disappearance of its primary disperser. Without mammoths, groundsloths, and other megafauna to transport its seeds uphill, the range of the species gradually shrank to the Red River region. In fact, fossils tell us that Osage-orange was much more widespread and diverse before the megafaunal extinctions. Back then, Osage-oranges could be found north up to Ontario, and there were seven, not just one, species in the Osage-orange genus, Maclura.

Another anachronistic tree is the Kentucky coffeetree, so named because early Kentucky settlers used its beans as a coffee substitute. Coffeetrees have tough, leathery pods with large, toxic seeds surrounded by a sweet pulp. Water cannot penetrate the thick seed coat to begin germination unless it is abraded or cut. Sounds like mammoth food to me. The natural range of coffeetrees is concentrated in the Midwest, but without its megafauna disperser, it is generally rare and mostly limited to floodplains.

Much the same can be said about the honeylocust, with its sweet seedpods up to 18 inches long. It is more common than coffeetrees, and is found in upland areas because cattle have filled in for the mastodons, camels, or some other dearly departed megamammal with a sweet tooth. The big-fruited pawpaws, persimmons, desert gourds, and wild squash may also have been dispersed more efficiently by recently extinct mammals.

Now when you see an Osage-orange, coffeetree, or honeylocust, you might sense the ghosts of megafauna munching on treats made just for them.

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11 Feedbacks on "Osage Oranges Were Made For Megafauna"

boligat

The megafauna may be gone, but the fruit still migrates uphill. In our neck of the woods, the Ozarks, that happens whenever the boys get into an osage orange fight. The fruit flies everywhere! Boy, does it sting when you get hit, too!



Walter Olson

They have some merit as a component of table centerpieces and mantel decorations, what with their striking looks and subtle scent.



LibertyorWHAT

In Kentucky we call them “hedge apples.” Horses will nibble on them occasionally but can’t eat them. This article was informative, I could never figure out what purpose they served.



Surellin

I see that a Russian/Korean team is injecting mammoth DNA into elephant eggs, attempting to bring back the mammoth. When they do, we can try them out on hedge apples.



Grover Joseph Rees

This would also help to explain the durian: http://www.durian.com . Although it is beloved of Southeast Asians (including many Vietnamese-Americans) and of Alfred Russell Wallace, author of The Malay Archipelago and discoverer of the Wallace Line, most other people really hate it. My wife defends its reputation as the “king of fruits” because it is said to be the only fruit tigers will eat. I think this is because it is the only fruit that smells like rotting flesh.



David

The osage orange isn’t a citrus; it’s a member of the mulberry family.



Dennis

David, the “orange” moniker likely came from the appearance of the fruit’s exterior, which is reminiscent of a large, green, “extra-bumpy” navel orange.



JDZ

sigh! I knew I ought to be looking up whether it is really a citrus, but I was sooo sure!



duane

where in va/ are these trees found towns etc id like to see one up close tyvm



maureen

In searching for natural spider repellants as I have a basement tenant who is freaked by the glue trap method of capture, I discovered Osage Oranges, called Hedge Apples some places, are used to repel insects, including spiders. Homeowners are said to place them along the permimerter of the home and in garages and windowsills and in displays inside to reduce and in some cases reportadly eliminate insect pests. I live in Purcellville VA and recall collecting these at from the local area with girl scouts around Christmas time to make ornaments by sticking cloves in them which is what was done 100 years ago. I know I have seen them at the Oatlands Plantation in VA.



Anthony

In Oklahoma and Parts of Kansas at least, the squirrels do a pretty good job eating them once they start to become over ripe.



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