Monday, October 19, 2020

A Camellia with a Secret and Woolly Mammoth Ghosts | Story Hunting at the National Arboretum

Yesterday we took a stroll through the National Arboretum, one of our favorite green spaces in the area. Not only did we enjoy perfect weather, see some pretty flowering things and get pics of bees at work, we got to experience two botanical wonders first hand.

I give you Lu Shan Snow, or as he (or she?) was originally known: Plant Introduction #162475:

While Lu appears to me as a fine botanical specimen, what really made Lu shine was a hidden super power that lay dormant for nearly 30 years. Here's the story:

Fifty years ago, Camellia seeds designated only as plant introduction (PI) number 162475 traveled from China to make their American debut at the U.S. National Arboretum in Washington, D.C.

The seeds were started in a greenhouse. But the resulting small trees had simple, white flowers and weren't as exciting as their showy, colorful cousins, Camellias sasanquas. So poor little PI 162475 was planted on a lower, less-traveled path, surrounded by the other trees.

The unremarkable camellia was soon forgotten.

But 30 years later, severe winter storms killed the neighboring C. sasanquas. In all, the harsh winters of 1977 to 1979 annihilated more than 950 camellias in the arboretum's Asian garden.

When the stately C. sasanquas lining the lower path were killed, PI 162475 was revealed. Not only did it survive, but it graced the garden with snow-white blooms in the following years. Later, this plain but strong-willed survivor would become the ancestor of a colorful, new cold-hardy camellia dynasty.


The second plant to catch my eye didn't have a fancy plaque or backstory. In fact, it was well camouflaged as a nebish, leafless, tree. I approached it because it looked so plain, I figured nobody else had shown it any love recently. When I got close to the trunk, it revealed and oddity: massive thorns. Check them out:

Ouch. I took a picture of the tree's attached metal tag and promised I'd look it up when I got home.

A quick Google Search explained that the Gleditsia triacanthos I found was more commonly known as a honeylocust. The tree's remarkable story revealed itself when I posed the question: what's up with its massive thorns? The answer: to keep wooly mamoth's at bay. As odd as this explanation sounds, it has science to back it up:

Consider the fruit of the Osage-orange, named after the Osage Indians associated with its range. In the fall, Osage-orange trees hang heavy with bright green, bumpy spheres the size of softballs, full of seeds and an unpalatable milky latex. They soon fall to the ground, where they rot, unused, unless a child decides to test their ballistic properties.

Trees that make such fleshy fruits do so to entice animals to eat them, along with the seeds they contain. The seeds pass through the animal and are deposited, with natural fertilizer, away from the shade and roots of the parent tree where they are more likely to germinate. But no native animal eats Osage-orange fruits. So, what are they for? The same question could be asked of the large seed pods of the honeylocust and the Kentucky coffeetree.
In the case of Cassia grandis, Janzen and Martin figured that the foot-long woody seed pods were eaten for their sweet pulp by giant ground sloths and elephant-like gomphotheres. These multi-ton animals had such big gullets that they didn’t need to chew a lot, so most of the seeds passed through the animals unharmed and ready to propagate more Cassia grandis trees. However, the gomphotheres and giant groundsloths disappeared about 13,000 years ago, toward the end of the last Ice Age of the Pleistocene.

Gomphotheres and ground-sloths? The Ice Age? What, you may be wondering, do they have to do with Osage-oranges, honeylocusts, and coffeetrees today?

In terms of evolutionary time, the difference between 13,000 years ago and now is like the difference between Friday, December 31, 1999 and Saturday, January 1, 2000. We may assign those two days to different centuries or millennia, but they are still part of the same week. Likewise, all the animals and plants of 13,000 years ago belong just as much in the present. In fact, they still live in the present, with just one major exception: most of the big and fierce animals are now gone. This happened just a couple thousand years before we invented agriculture and planted the seeds of civilization. Woolly mammoths actually survived on some Arctic islands until after the Egyptian pyramids were built!
Now when you see an Osage-orange, coffeetree, or honeylocust, you might sense the ghosts of megafauna munching on treats made just for them. (You may even see tropical ghosts in your local grocery store hungrily eyeing the avocados and papayas.) But you can also conjure megafaunal ghosts by considering the weapons designed by trees to discourage or slow their big mouths from eating the foliage.

Osage-orange, mesquite, and hawthorn all bear stiff thorns, spaced too widely apart to do much good against narrow deer muzzles, but they would be unavoidably painful in the wide mouths of groundsloths and mastodons. Wild honeylocusts have vicious, trident-like thorns several inches long covering the lower trunk and branches.

So there you have: the honeylocust is ready to defend itself against a multi-ton animal that no longer exists. Amazing.

And such is the joy of the Arboretum: it's equal parts hiking and picnic destination as well as holder of remarkable sights and stories. Come for the former, and search for the latter.

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