Hunting the first flower
Posted: Tuesday, April 17, 2007 7:45 PM by Alan Boyle
If you're looking for the traces of the first humans, you go to Africa. But if you're looking for the mother of all gardens, you go to China. At least that's what botanists and film crews did for "First Flower," an exotic blooming documentary that premieres on public television tonight.
The "Nova" episode weaves two stories together: One is an easy-on-the-eyes expedition to China's Hengduan Mountains, considered the most biodiverse temperate forest on Earth. This is where plant explorer Dan Hinkley (the Indiana Jones of the plant world, according to the "Nova" team) meets up with Chinese botanist Yin Kaipu to document just some of the region's tens of thousands of plant species.
Doug Hamilton / WGBH Science Unit |
A wild alpine flower blooms in
China's Hengduan Mountains.
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The Hengduan Mountains are where many of our best-loved flowers, including the classic regal lily, got their start. Because of its unusual and varied topography, the region served as an ancient "safe deposit box" for flowering species that were wiped out elsewhere by Ice Age glaciers.
China's colorful blooms - ranging from all sizes of rhododendrons to the rare lady's slipper orchid - are visual knockouts that deserve every one of Hinkley's on-camera exclamations of wonder.
It's hard to compete with all that splendor, so I don't envy University of Florida paleobotanist David Dilcher, who helps tell the other half of the TV tale. While Hinkley is feasting his eyes on present-day posies, Dilcher is digging into the fossil record of plants from the late Jurassic and early Cretaceous periods.
Dilcher focuses on specimens unearthed by Chinese colleague Sun Ge and his team in northern China's fossil fields. The researchers made a splash nine years ago when they identified a fossilized plant that appeared to have enclosed seeds - which is the tip-off for a flowering plant.
Doug Hamilton / WGBH Science Unit |
Sun Ge, a paleobotanist from Jilin University in China, and David Dilcher, a
paleobotanist from the University of Florida, search for fossils of flowering plants in
northern China. Their quest is chronicled in the "Nova" documentary "First Flower."
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Sun, Dilcher and their colleagues initially thought the specimen, designated Archaefructus liaoningensis, dated back 140 million years. That would be a jaw-dropper, making Archaefructus the earliest known flower by far. A controversy erupted, of course, and radiometric dating later led the researchers to adjust the age to 125 million years. "First Flower" traces the whole debate, but the bottom line is that Dilcher isn't so interested in claiming dibs on the "first flower."
"I don't really like words like 'first,' 'only' and 'earliest,'" he told me Monday. "You know it won't be more than a few years or a few months before it's pre-empted. ... Of course, just as truth would have it, thre's now more than one 'first flower' in the world, and there will be even more 'first flowers' in the world. We'll wind up with a bouquet after a while, and we'll need to sort through these."
Dilcher is more interested in the characteristics of early flowers, whether they're 140 million years old or 125 million years old. That study quickly leads to deep questions. For instance, considering that it takes so much energy for plants to put out flowers, why do they even bother?
"When I was a student, I was taught that the magnolias and such plants closed their seeds inside their fruit because the insects that came to visit these flowers would eat the young, unfertilized or newly fertilized seeds," Dilcher said. "That seemed like a good explanation. But I don't accept that any more. I think that the insects certainly are progressive enough that they can develop tearing and boring devices with their mouth parts, so the protection is very nominal."
Dilcher said the "why" might have more to do with flower sex ... and evolution.
First, let's talk about the sex: To encourage genetic diversity, the male and female parts of a flower - that is, the stamen and pistil - are positioned in such a way to minimize the chance of self-fertilization. Dilcher suspects that each flower has subtler mechanisms as well to differentiate between its own pollen and the more desirable pollen from other plants.
There are plenty of opportunities for the Darwinian survival of the fittest to play a role in flower development. Just as sperm compete to fertilize the egg, grains of pollen compete by sending down tubes to fertilize a flower's ovule. "The fastest-growing pollen tubes give rise to the best and most vigorous seeds," Dilcher said.
Over the course of millions of years, the more successful flowers came to manage the behavior of insects to maximize genetic diversity.
"The flowering plants are a product of what we call co-evolution," Dilcher said. "They really took off with the visits of insects and outcrossing. The first flowers were not attractive, but they may have offered pollen for food. They may have offered up a nectarlike material. And then some flower got the idea that if it pulled a leaf up and turned it white or red, that would attract more of these visitors."
Early flowers could document how all this got started. "As we find more evidence, and as we zero in on the characters, we may begin to change our image of what we're looking for," Dilcher said.
Although they're not as colorful as a red, red rose, the fossils of long-past flowers could provide insights into how evolutionary pressures such as climate change will affect future flowers. And we're not talking just about roses and orchids here - but also about the flowers we depend upon for our daily bread. After all, wheat, corn and rice are flowering plants, too.
