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.
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.
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.
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