September 23, 2020

Lina Tran

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Our Loneliest Native Fruit

One more on pawpaws, featuring endozoochory and the woolly mammoth

When late summer yawns into fall, give the right tree along a riverbank a gentle shake, and a pear-green, bean-shaped fruit may fall to the ground with a soft thud. The reputation of the pawpaw—the continent’s largest native fruit—does not often precede itself. The pawpaw is hard to cultivate for the market. Its season and shelf life are limited, and it bruises easily. But the flavor is worth the coddling. It tastes like someone blended mango, banana, and pineapple into a soft custard. When pawpaws are ripe, they exhale yeast and flowers, like a summery wheat beer.

The pawpaw can handle our falls and winters, unlike its tropical cousins, the cherimoya and soursop. Like those cousins, though, it is missing something key to its identity as a fruiting tree: the group of animals meant to eat and spread it.

Our Loneliest Native Fruit - Quote

Some things don’t quite fit in the present, like corsets, pocket watches, or MySpace. Ecology has anachronisms, too: species missing their evolved partners, which have since gone extinct.

Since they can’t roam themselves, most trees rely on animals to spread their seeds afar. Over time, trees and animals forge partnerships. Ecologists call it endozoochory. Trees grow inviting fruit and animals gobble it up, wandering off after their meal with precious seeds in their bellies. The seeds, still intact, rollercoaster through animals’ digestive systems. All a fruiting parent wants for its children is to fall far from the tree, preferably in a pile of hot dung.

Some things don’t quite fit in the present, like corsets, pocket watches, or MySpace. Ecology has anachronisms, too: species missing their evolved partners, which have since gone extinct. Pawpaws date back to the Miocene, some 5.3 to 23 million years ago, when huge, vegetarian creatures like mastodons and woolly mammoths trudged across the continent. Pawpaws lured them in with sweet, fatty flesh—the creme brulee of the fruit world.

The mass extinction of North America’s largest mammals, which came about 10,000 years ago, was quick—a one-two punch of climate change and overhunting. Evolution is slow. Millennia ago, pawpaw trees kept our mighty mammals fat and happy. To this day, they’re still cooking, but the giant beasts are never home for dinner.

Forty years ago, tropical ecologist Daniel Janzen explained anachronisms like the pawpaw. Piles of fruit languishing in Costa Rica’s rainforests caught his attention. Trees spent all their time and resources bearing lush fruit with hardy seeds, he observed, only to let them fall and rot in their parents’ shadow. Why should trees waste energy producing fruit when no animals come to eat them? The answer, Janzen proposed, was that their animal partners were no more.

Without assists from hungry megafauna, pawpaws’ growth range likely took a hit. Although today’s deer, raccoons, and other smaller mammals nibble on pawpaws, they can’t spread the seeds like the mammoths that likely dispersed the trees across the heartland. Luckily, pawpaw trees can reproduce without seeds. They clone themselves with root suckers, identical shoots that sprout up to form dense patches.

I found one such pawpaw patch on my last trip into the woods. Their leaves drooped like palms, and their spindly branches bowed under the weight of their fruit. Walking around the ring, I nudged the slender trunks. When pawpaws are ripe, they readily drop. These days, foragers don’t leave much fruit to rot. Happily, we take advantage of the tree’s ignorance. I jiggled a tree in a quiet patch, and a pawpaw the size of a baked potato came plummeting down, bouncing off my glasses. Tears leaked from my eye. My hunt was done for the day. Surely, a mastodon wouldn’t have minded as much.


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