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A Plant With Smarts

  • By Susan Orlean
  • Posted 11.01.02
  • NOVA

The orchid family could have died out like dinosaurs if insects had chosen to feed on simpler plants and not on orchids. The orchids wouldn't have been pollinated, and without pollination they would never have grown seeds, while self–pollinating simple plants growing nearby would have seeded themselves constantly and spread like mad and taken up more and more space and light and water, and eventually orchids would have been pushed to the margins of evolution and disappeared.

Instead, orchids have multiplied and diversified and become the biggest flowering plant family on Earth because each orchid species has made itself irresistible.

Bamboozling bugs

Many species look so much like their favorite insects that the insect mistakes them for kin, and when it lands on the flower to visit, pollen sticks to its body. When the insect repeats the mistake on another orchid, the pollen from the first flower gets deposited on the stigma of the second—in other words, the orchid gets fertilized because it is smarter than the bug.

Another orchid species imitates the shape of something that a pollinating insect likes to kill. Botanists call this pseudoantagonism. The insect sees its enemy and attacks it—that is, it attacks the orchid—and in the process of this pointless fight the insect gets dusted with orchid pollen and spreads the pollen when it repeats the mistake.

Over the eons, orchids have bent over backward coming up with new tricks to entice insects. This orchid, Renathera storiei, a native of the Philippines, relies on a red so rich it seems dabbed on. Enlarge Photo credit: ©Kevin Schafer/CORBIS

 

Other species look like the mate of their pollinator, so the bug tries to mate with one orchid and then another—pseudocopulation—and spreads pollen from flower to flower each hopeless time. Lady's slipper orchids have a special hinged lip that traps bees and forces them to pass through sticky threads of pollen as they struggle to escape through the back of the plant.

Another orchid secretes nectar that attracts small insects. As the insects lick the nectar they are slowly lured into a narrowed tube inside the orchid until their heads are directly beneath the crest of the flower's rostellum [an extension of the stigma, the part of a flower on which pollen germinates]. When the insects raise their heads the crest shoots out little darts of pollen that are instantly and firmly cemented to the insects' eyeballs but then fall off the moment the insects put their heads inside another orchid plant.

The harmony between an orchid and its pollinator is so perfect that it is kind of eerie.

Some orchids have straight–ahead good looks but have deceptive and seductive odors. There are orchids that smell like rotting meat, which insects happen to like. Another orchid smells like chocolate. Another smells like an angel food cake. Several mimic the scent of other flowers that are more popular with insects than they are. Some release perfume only at night to attract nocturnal moths.

No one knows whether orchids evolved to complement insects or whether the orchids evolved first, or whether somehow these two life forms evolved simultaneously, which might explain how two totally different living things came to depend on each other. The harmony between an orchid and its pollinator is so perfect that it is kind of eerie.

Flower power

Darwin was very interested in how orchids released pollen. He experimented by poking them with needles, camel–hair brushes, bristles, pencils, and his fingers. He discovered that parts were so sensitive that they released pollen upon the slightest touch, but that "moderate degrees of violence" on the less sensitive parts had no effect, which he concluded meant that the orchid wouldn't release pollen haphazardly—it was smart enough to save it for only the most favorable encounters with bugs.

He wrote: "Orchids appeared to have been modelled in the wildest caprice, but this is no doubt due to our ignorance of their requirements and conditions of life. Why do Orchids have so many perfect contrivances for their fertilization? I am sure that many other plants offer analogous adaptations of high perfection; but it seems that they are really more numerous and perfect with the Orchideae than with most other plants."

One orchid pod has enough seeds to supply the world's prom corsages for the rest of eternity.

The schemes that orchids use to attract a pollinator are elegant but low–percentage. Botanists recently studied 1,000 wild orchids for 15 years, and during that time only 23 plants were pollinated. The odds are bad, but orchids compensate. If they are ever fertilized, they will grow a seedpod that is supercharged. Most other species of flowers produce only 20 or so seeds at a time, while orchid pods may be filled with millions and millions of tiny dust–sized seeds. One pod has enough seeds to supply the world's prom corsages for the rest of eternity.

Some species of orchids grow in the ground and others don't live in soil at all. The ones that don't grow in soil are called epiphytes, and they live their lives attached to a tree branch or a rock. Epiphytic orchid seeds settle in a comfortable spot, sprout, grow, dangle their roots in the air, and live a lazy life absorbing rainwater and decayed leaves and light. They aren't parasites—they give nothing to the tree and get nothing from it except a good place to sit.

Who needs earth when you have air? This epiphytic orchid, Paphiopedilum esquirolei, lives high in trees found in northern Thailand and southern China. Enlarge Photo credit: ©Greg Allikas

 

Most epiphytes evolved in tropical jungles, where there are so many living things competing for room on the jungle floor that most species lose the fight and die out. Orchids thrived in the jungle because they developed the ability to live on air rather than soil and positioned themselves where they were sure to get light and water—high above the rest of the plants on the branches of trees. They thrived because they took themselves out of competition.

If all of this makes orchids seem smart—well, they do seem smart. There is something clever and unplantlike about their determination to survive and their knack for useful deception and their genius for seducing human beings for hundreds and hundreds of years.

Susan Orlean Susan Orlean has been a staff writer at The New Yorker since 1992. This article was excerpted from her book The Orchid Thief: A True Story of Beauty and Obsession, ©1998 Susan Orlean. Used by permission of Random House, Inc.

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