Mastodons in Manhattan: How the Honey Locust Tree Got Its Spikes

Walking south in Riverside Park, somewhere around 91st Street, the ground is littered with long brown  seed pods, some with visible bumps inside, like giant pea pods.

The tree trunks sport spikes, sharp and menacing.

“Aha,” I think, reaching for a nugget of knowledge given to me many years ago by my 5th grade best friend, Janet. “Carob trees. People make fake chocolate with the pods.”

Back at home with my trusty tree guide, I discover the tree is actually a honey locust tree (Gleditsia triacanthos), a relative of the carob.  Both are members of the legume family, and the pods are indeed giant pea pods. The honey locust derives the “honey” in its name from the sweet taste of a gummy edible paste that surrounds the protein-packed peas inside the pods.  The pods are eaten by livestock, including horses, cattle and pigs, as well as squirrels, rabbits, deer and birds.

Now about those stegosaurus-like spikes. The spikes are an arboreal defense mechanism to keep herbivorous predators from browsing the tasty trees.

Fascinating to realize that herbivores, prey for carnivorous predators, are themselves  predators of plants. Since trees can’t run away or attack with tooth and claw, their defenses are stationary, usually involving tough bark, leathery leaves, a variety of sharp thorns and spikes, and even bad smells. Some acacia trees have evolved a symbiotic relationship with fierce stinging ants. The trees provide special food and shelter for the ants, which bite any animal that tries to browse the leaves and shoots.

Which way to the honey locusts?

The honey locust co-evolved with giant herbivores, its impressive spikes serving to protect it from the browsing mastodons and woolly mammoths that roamed North America, including  Manhattan, until somewhere between 6,000 and 11,000 years ago. The tree has not yet lost the adaptation, still sprouting spikes sharp and tough enough to puncture a truck tire. Or a mastodon tongue. They’ve been used as nails and blowgun darts, and Civil War soldiers used them to pin together torn garments.

The honey locust withstands pollution, drought and poor soil. According to New York City Trees: A Field Guide for the Metropolitan Area, the honey locust is the most common street tree in Manhattan. The trees in full leaf are said to provide a lovely dappled shade. I look forward to walking beneath one in midsummer.

For more on plants and evolution at Out Walking the Dog, read The Burry Man, The Burry Dog and Burdock. For a monthly round-up of up-to-the-minute evolutionary science blogs, check out The Carnival of Evolution.

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28 Comments on “Mastodons in Manhattan: How the Honey Locust Tree Got Its Spikes”

  1. Alan Says:

    Poor likeness of a Mastodon. Their tusks aren’t curved up like that. Those look more like elephant tusks.


    • Oh dear. Well, it is certainly an old-school illustration, but the fossils I’ve seen do have tusks that curve upwards. Maybe with that hump on its back it’s a mislabeled woolly mammoth? Or maybe it’s just a poor artist’s rendition, or an artist’s poor rendition. Will have to re-research … Feel free to post more info!

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  3. Martin Wong Says:

    I really have learned a great deal from reading your blog! keep on going! I am looking forward to reading even more!

  4. Roseann Says:

    We have honey locust trees (thornless) here in SW Wisconsin. The honey locust is being featured as Brodhead’s September Tree of the Month! You’ve really helped with my research – thanks!

  5. Laura Harkins Says:

    Hello,

    I was hoping to use the mastadon picture up there for a research project and I was wondering where it came from. I would like to be able to credit it properly.

    ~Laura


    • Laura, I found that mastodon image on a website where it was listed as being free of copyright restrictions. There was no other information. SHould you (or any other reader) discover the name of the illustrator or any other info about the source, please let me know. I’d like to credit the picture properly. Good luck with your research project.


  6. Very cool post! I had no idea the pods were sweet. I’ve tried to give them to the squirrels many times, but they reject them out of hand. My dog Jolly, however, thought the pods made an excellent toy. Those spikes are so scary looking I’m always amazed the city didn’t ban planting them here like they do so many other species.

  7. Squirrel Says:

    Very interesting, I see Honey Locust all the time but never took a moment to learn about it and I love to learn new things. Thanks so much. I’m going to scroll down and read more of your posts.

    • Melissa Says:

      Thanks, Squirrel. Honey locusts turn out to have such an interesting history but who knew? Certainly not me, until I started researching them.

  8. Georgia Says:

    Great post Melissa! I found your blog via FOTT 46.

  9. rebecca Says:

    Very cool! I’ve always loved the ferociousness of honey locust spikes, but it never occurred to me that they would have evolved in response to ancient North American plant predators like mastadons, despite having once written an entire paper in college on the ecology of plant thorns and spines.

  10. Jacqueline Says:

    I loved this post. My Council would not dare to plant a tree like this. Far too worried about Public Liability. Hence I have never seen anything like this. I would have a stack of the seed pods somewhere in my home. They look beautiful. It’s amazing that a tree can stay ‘original’ for many thousands of years.
    We have four old trees in a park which a local Indian family say are Carob. They look knobbly as though diseased, but the family say the trees are quite healthy. Every year the family come down to the park at night & harvest for Carob. Soon they will all be chopped down for a circular cement path.

    • Melissa Says:

      Thank you, Jacqueline. I believe most (all?) honeylocusts sold today are thornless. Interesting about the Carob trees. I wonder what the family makes with the seed pods. Do you know? Sad that the trees will be cut down.


  11. [...] Out walking the dog, Melissa Cooper discusses Mastodons in Manhattan: How the Honey locust Tree Got Its Spikes, noting that the formidible thorns of the honey locust tree are remnants of its co-evolution with [...]


  12. Fascinating stuff, Melissa. I’ll be looking out for the spikes on my next trip to the park.
    Avi

    • Melissa Says:

      Thanks, Avi. When you see those giant pods on the ground, look up. Between 80th & 91st or so, there seem to be tons of honeylocusts, but none up past 108th Street.

  13. katrinka Says:

    You will have a treat when these guys are in flower. I’m not sure if it’s these thorny ones or the many other acacia or pseudo-acacias around the park, but the perfume is absolutely unequalled in my opinion. They flower like mad too. I grew up with three in Montreal (no thorns) and can’t get enough of that sweet scent.


  14. There are thornless cultivars that are now planted as street trees. They don’t need to worry too much about herbivores along the sidewalks.

    • Melissa Says:

      True, although the Ringling Bros. elephants did just make their annual pilgrimage on-foot from Queens to Madison Square Garden. Giant herbivores in Manhattan – put up your spikes! I suppose most (all?) of the trees sold now are thornless, but their story’s no fun.

  15. Joy K. Says:

    I’ve punctured tires, feet, and knees with those spikes. These are not the trees you want overhanging your driveway, dappled shade or no dappled shade.


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