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Ginkgo leaf. Photo by monteregina. Visit the photo slideshow.

Ginkgo leaf. Photo by monteregina. Visit the photo slideshow.

KUOW News

Birds And The Bees

Sarah Waller
03/19/2012

Some people might get a little pink in the cheeks when discussing the birds and the bees. Today, we head to a quiet neighborhood near Green Lake where a surprising romance is, quite literally, in the air. Sarah Waller has the story.

TRANSCRIPT

Film: "Some of you may become somewhat uncomfortable as parts of this unfold. But I think, unless you're an extremely unusual audience, you will welcome some of this insight."

They stand side–by–side. One's tall, the other is more slender. They lean in toward each other, almost touching. There's a reason why Arthur Lee Jacobson has taken me to this particular spot.

Jacobson: "There's only a handful of places in Seattle where you can see both a male and a female together."

We're talking about trees — ginkgo trees. You can pick them out by their triangular, fan–shaped leaves. Ginkgos are very common in Seattle, but they're capable of some pretty uncommon things.

Arthur has written about them in his book "Trees of Seattle." He says the first thing that sets ginkgos apart is their sex.

Most trees are what scientists call monoecious, meaning a single tree has both male and female parts.

Jacobson: "Most trees are bisexual. But there are a minority of trees, maybe 10 or 15 percent, where they are strictly male or they're female."

And ginkgo trees are one of them.

Sarah Waller: "So which one is which here?"

Jacobson: "The female is definitely broader, just like human females — at least at the hips are broader — but the male is slender. It's sort of like a human; the reproductive parts are what you look at."

So we did look at them. And just like your human sexuality class in junior high, Arthur's description of ginkgo anatomy gets a little graphic.

Jacobson: "The boys have these dangling things that release the pollen, and the females have these little things about the size of a radish seed that are glistening and wet saying, 'Pollen come here, pollen come here,' in tree language."

The parallels between human and ginkgo tree sex get even stranger, especially when you take a microscopic look at the male reproductive cell: a grain of pollen.

Jacobson: "Unlike most plants, it's more like an animal. It can crawl, or swim, or whatever."

Ginkgos are the only trees with free–swimming sperm. Here's how it works: Wind blows pollen from a male tree onto the sticky parts of a female tree. Those sticky parts are attached to egg cells. When a grain of pollen lands, it releases two sperm cells. Like human sperm, they can swim. They head straight for the egg.

The fastest sperm fertilizes the egg, and a new ginkgo embryo begins to form. It's surrounded by a soft, fleshy substance called sarcotesta. It looks like a fruit, but is actually a nut. And that fleshy nut is the reason why most ginkgo trees in Seattle are male.

Jacobson: "It's rare to find female ginkgos because most people think the fruit is messy and it stinks."

One of those people is Maresi Nerad. She owns the house next to these two ginkgo trees. She likes them, but sometimes they can be a nuisance.

Nerad: "Because the fruit, when it's on the ground, smells."

Waller: "What's it smell like?"

Nerad: "Well, it smells like someone has thrown up (laughs)."

Jacobson: "Vomit, bad body odor, dog poop; You get the idea. It's disgusting."

Nerad: "Really, it's not a particularly good smell."

Because of that odor, most people plant male trees. People like them because they are gorgeous in the fall. Both sexes turn a bright butter yellow. And they are resilient. They make great urban trees because they can tolerate high levels of air pollution.

They have even been known to withstand an atomic bomb. Six ginkgos were among the only living things to survive near ground zero in Hiroshima. In fact, these trees are considered living fossils. They've been around for millions of years.

Jacobson: "When there were still dinosaurs and tall ferns and horsetails everywhere, the ginkgo was here. It's a survivor, and that commands respect."

Maybe it's the ginkgo's resilience and longevity that make it a popular health food. You'll find ginkgo biloba on the herbal remedy aisle of most grocery stores. Some people say it boosts memory, other people claim it's an aphrodisiac, which brings us back to the topic of sex.

Film: "We have tried to bring out facts not well understood and have tried to explain them on a scientific basis."

So, next time you pass under a tree with distinctive fan–shaped leaves, look up. A courtship between an egg and a wiggly–tailed tree sperm may be taking place right over your head.

I'm Sarah Waller for KUOW.

© Copyright 2012, KUOW

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