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DECEPTIVE BEAUTIES

The World of Wild Orchids

THE UNIVERSITY OF CHICAGO PRESS

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CHAPTER 1

ADAPTATION

They captivate with their beauty and seeming fragility, yet orchids belong to one of the hardiest, most adaptable plant families on Earth. With some 80 million years of evolution in their past, they've evolved to survive and thrive in a host of habitats, from semideserts to humid mangrove marshes, from the high hot canopy of tropical forests to the barren coldness of arctic tundra.

AN EVOLVING STORY

As a young naturalist growing up in southwest Germany, I was enthralled by orchids. To me, they were wondrous, exotic, and rare. When I roamed the early summer hills in search of wildlife and plants, spotting an orchid was always a particular thrill. I had learned where to look for them from a neighbor who was very botanically inclined. He knew the exact places along roadways where little patches of orchids flourished, despite the fact that they had no business being there. He guessed that they had arrived at their particular spot when the road was being built and a bit of limestone soil containing orchid seeds had found its way into the road margins. Since many of these terrestrial orchids need limestone, I would also look for them in sward—sparse, poor meadowland that drains well. Orchids, I soon realized, had flowers that didn't look like other flowers, and various species of these lovely, delicate works of nature could thrive in almost any environment, from rocky barren sward to shady wetlands.

I clearly remember a college field trip to a rolling grassland not far from my university. We had come at exactly the right week in late May and found a good dozen species of pink orchids of the genus Orchis in the south-facing sward. Then we walked up the meadow toward the vast Palatinate Forest, which runs all the way to the border with France, and there in the half-shade of the beeches along the forest edge were the delicate orchids called little white forest birds. Going deeper into the Palatinate, we found swamp orchids by a creek and in dark patches of woodland, brown orchids with none of the chlorophyll that gives most plants their greenness. This variety, called the bird's-nest orchid, lives off the nutrients it receives from a symbiotic fungus.

No other plant family held quite the same fascination for me as orchids did, maybe because of their relative rareness in northern Europe and certainly because of their unusual appearance—their delicate shapes and configuration, the deep spurs that hide their nectar. They weren't structured like any other flowers, and they seemed somehow special in a mysterious way.

As the radius of my wanderings expanded, I had the opportunity to see some amazing orchid habitats across Europe. On a backpacking trip into the Swiss Alps I saw orchids in abundance for the first time. I was astonished at the profusion of their blooms across the high mountain meadows, their pink spikes glowing amid dozens of other summer flowers and all of it backdropped by snow-capped peaks. It was breathtaking. There were at least a dozen species in those meadows, including the pyramid orchid that Charles Darwin had studied and written about. An orchid enthusiast himself, Darwin gathered wild orchids near his home in Kent and propagated them. In fact, orchids inspired some of his most critical thinking on natural selection. In his book The Various Contrivances by Which Orchids Are Fertilised by Insects, he explains the co-evolution of insects and orchids and calls them "amongst the most singular and most modified forms in the vegetable kingdom."

I shared Darwin's enthusiasm for these "singular" creatures, and on hikes I took into the Pyrenees, southern Italy, and Greece, I discovered a whole new realm of orchid species that I had not seen before. Some of them were oddly shaped, mimicking bees and other insects, while others grew to amazing sizes and had a sweet, honeyed scent.

In graduate school, on botanical research expeditions in the tropics of Asia, Africa, and Panama, I began to realize how narrow the European range of orchids was. Tropical orchids seemed nothing like the ground-based European varieties I had known. Almost all orchid species in the warm rain forests lived as epiphytes, growing from other plants, often high up in the canopy. The shapes, colors, and, in many cases, the scents, were out of this world. Their diversity seemed endless; hardly ever would I find two individuals of the same species.

My experience with orchids mirrors the global patterns of orchid distribution. While temperate areas tend to have fewer species and predominantly terrestrial ones, tropical orchids are much more diverse and most are epiphytic. Central Europe has about 250 species of orchids, yet Panama, barely one-tenth the size, has more than 1,300 known species, with many newly discovered ones being reported every year.

That's typical of the difference between tropical and temperate places worldwide, and the explanation for this lies deep in the Earth's past, in its geology and weather patterns.

KEEPING AHEAD OF CLIMATE CHANGE

For the 3.5 billion years that life has existed on Earth, this has been a warm planet, meaning most life probably evolved under conditions even warmer than what now exists in tropical areas. The giant fern and horsetail forests that prevailed some 36o to 300 million years ago in the Carboniferous period evolved and flourished in a hot, moist climate. Over the course of many millions of years the organic deposits from these plants created the carbon fossil fuels—coal and oil—that we rely on today.

Modern flowering plants began to emerge about 140 million years ago in the Cretaceous period. By 100 million years ago, they had diversified widely, probably coevolving with insects—the insects pollinating the flowers and the flowers feeding the insects. The first orchids are thought to have appeared around 80 million years ago, among the flowering plants of the tropical forests. It's amazing to think of orchids as coexisting with dinosaurs and yet the two shared the planet for a good 15 million years.

The tropical forests of today have existed and evolved without major interruptions for millions of years. Some, like the rain forests in parts of Africa and South America, date back an astonishing 65 million years. Of course they started with a different and less diverse set of species, but these ancient, persisting habitats are more likely to preserve species over time. That's why the majority of orchid species still inhabit the tropics. And the greater number of potential pollinator species in these forests has probably added to the orchids' evolutionary potential, accounting for the species richness closer to the Equator, while the numbers drop off sharply toward the poles.

In contrast, temperate habitats are much younger and have been subject to more intense temperature variations that can occur even yearly. Orchids have survived only as terrestrial species, so they can retreat underground during inclement seasons.

Climatic changes have occurred throughout the Earth's history, and they've never been evenly distributed, always affecting the poles much more than areas close to the Equator. Today, in fact, the polar regions of Earth are warming up at an alarming rate, while the increase in temperature is happening at a much slower pace closer to the Equator. During past periods of cooling, large areas of the temperate zone—a good part of which lies in the present-day United States, northern and western Europe, and China—also cooled down significantly and were often covered with huge glaciers. Most species could cope with the gradual cooling of the planet, but the glaciation events were far more challenging, driving species and whole ecosystems south. In the past 500,000 years alone, there have been five such periods of glaciation, and once each ended, life had to start virtually from scratch in the north.

Central Europe, the region that I grew up in, has been hit especially hard by glaciation-induced extinctions, even by temperate zone standards. Fossils from Messel, a famous site close to Frankfurt in central Germany, point to the existence of a very diverse tropical forest there about 5o million years ago. Similar to what we find in Borneo today, this species-rich community included a wide variety of plant life, as well as crocodiles, monkeys, and many bat, bird, and large insect species. Since then, the entire planet has cooled and, due to the movement of tectonic plates, Europe has glided north about 800 miles (1,300 kilometers). Over time, the ecosystems and many of the species of tropical Europe have migrated toward the Equator.

These European migrants faced a serious challenge as they moved south: the Alps. Other continents have north-south-running mountain systems, but this east-west barrier often proved fatal for species on the retreat from approaching glaciations. Time and again, species got pushed against the Alps, and only the ones that could move fast enough to escape the ice and cold survived.

In plants these kinds of migrations require different processes than they do in animals. While animals for the most part can move as individuals under their own steam—walking, flying, swimming—plants have to find different solutions. The movement of plants takes place across generations, with each generation taking a single step, if the conditions are right. The movement phase in the life of plants is not in the adults, who are firmly set in a single place, but in the seeds. Seeds can cover amazing distances, many miles sometimes. The agents of transport can be abiotic, such as wind or water. More often animals take the role of dispersers, and seeds can travel long distances in the fur, feathers, or guts of animals. Wherever the seed is transported, it will attempt to germinate. But only those that end up in a habitat with just the right conditions become successful individuals of the next generation.

Imagine that a colder period is descending on the Northern Hemisphere. Over several hundreds or thousands of years, the average temperature slowly drops. For the plants of any given species adapted to that ecosystem, conditions keep getting worse on the northern edge of the area, while they keep getting better toward the south. Seeds that have been dispersed northward are less likely to be successful than the ones that end up toward the south. So the distribution of the species in this ecosystem is slowly, step by step with each generation, shifting toward the south.

It's obvious under this scenario that different plant species will have very different travel speeds, depending mostly on how long it takes them to produce a new generation and on their average seed-dispersal distance. While annuals disperse every year from their first year on and thus are able to respond quickly to climate changes, trees might have a generation time of ten or more years and can take a step only that often. This generally means that trees are slower responders to climate change than annuals, but in fact some trees make up for the long generation time by having efficient long-distance seed dispersal. In the case of epiphytic orchids, the plants bear huge quantities of minute, almost microscopic seeds that can be dispersed great distances by the wind. That allows for rapid transit and the opportunity to colonize new habitats.

Plants and plant communities flow north and south over time, following the ever changing climate. If climate change is very rapid, as it is now, some or even many species might not be able to move fast enough. They'll get run over by the changing conditions and sink into extinction.

The glaciations of the last million years have significantly influenced all Earth's temperate ecosystems. After all, a mere 15,000 years ago large areas of North America and Europe were covered with ice sheets. The temperate species of today either migrated up from the south or originated from protected habitat islands that were not ice-covered. The orchids of Europe and North America seem to be a mix of both.

As to the long-lived tropical forests, the periods of Earth's cooling had far less impact on them, manifesting mostly as a reduction in rainfall rather than a drop in temperature. In fact, the periods of cooling may have acted as "species pumps"—encouraging new species to evolve. Here's how it worked: Reduced rainfall turned parts of the jungle into savannah, interrupted by "islands" of forest. The habitat fragmentation isolated plant and animal species in these island communities, where they evolved new species. That helps explain the richness of flora and fauna in the tropics today and the vast diversity of orchids found there.

THE HIGH LIFE

The orchid family is exceptional, probably uniquely so, in its ecological diversity and its ability to tolerate environmental stresses of various kinds, especially a lack of nutrients and water. Members of the orchid family are able to live in a range of habitats—from semideserts to the moistest forests. Some species inhabit swamps and can even live as floating aquatic plants, while others flourish in alpine meadows and arctic tundra. Even when shrubs and trees have petered out in the harsher northern temperate zone or at high altitude, there are orchid species that hang on. In fact, orchids thrive in extreme habitats, pushing the edges of where plant life can exist on the planet.

Many orchids have evolved into epiphytes, plants that use others for structural support without being parasitic. Epiphytes have no connection to the ground and must therefore cover all their nutritional needs while attached to another plant. An estimated 72 percent of orchids, or 15,000 to 20,000 species, live in the canopies of rain forests, making them the plant family with the highest number of epiphytic members.

The epiphytic life form probably evolved in the orchid family many times independently, because the ancestral orchids had a set of important pre-adaptations that equipped them for life in the treetops and in other marginal habitats. Among these pre-adaptations were their drought resistance; their low nutrient requirements; their special, more water-efficient type of photosynthesis; and their ability to produce huge numbers of tiny, easily dispersed seeds. The big disadvantage of the epiphytic existence is the disconnection from the ground and thus from a steady and reliable supply of nutrients and, most crucially, water.

Despite the fact that tropical rain forests receive abundant rain, the living environment of an epiphyte high in the canopy can resemble a desert, with the stress of extreme heat, radiation, and photo bombardment from the sun. All epiphytic orchids have evolved a number of adaptations to cope with these conditions. Most have leathery leaves with a thick outer wax layer that reduces water loss and also protects the plant from the intense UV that could destroy proteins and DNA. They also have a modified root system, the roots covered with a spongelike layer of dead tissue called velamen. When it rains, the epiphytes' velamen captures water and stores it—an adaptation to the rare, short, and heavy downpours that occur in the dry seasons of tropical rain forests. Another water-storage adaptation among orchids is their thickened stems, called pseudobulbs, which store enough water to get the plant through a dry season. Orchids that produce pseudobulbs grow new ones each year.

While living high up in the canopy can have its stresses, this place in the sun is also the greatest advantage of the epiphytes. With very little investment in a stem, these plants have access to sunlight and can concentrate on gathering it with almost all their tissue. A tree, in contrast, has to invest a lot more to get its own leaves into the sun. Abundant sunshine is very beneficial for the process of photosynthesis, in which carbon (from atmospheric carbon dioxide) is captured by the plant. Probably the most important and sophisticated adaptation in orchids is their way of doing photosynthesis—a process called CAM, for Crassulacean Acid Metabolism. The defining feature of CAM is the ability to take CO₂ from the atmosphere at night and store it until day, when the energy of sunlight is available to turn carbon into sugars. On a molecular level, this happens when electrons are knocked free by the light and stored in energy-transporting molecules—much like the process in a solar panel. These molecules then provide the energy to build sugars from CO₂ and water. So CAM allows orchids to keep their leaf openings closed in the daytime, thus significantly reducing the loss of water.

Many scientists see these adaptations as a major reason for the impressive diversification of the orchid family. Drought resistance and low nutrient requirements enabled the terrestrial orchids of the temperate zones to colonize such difficult habitats as rocky, porous karst landscapes or nutrient-poor meadows and to diversify there. As to the tropical epiphytes, the ancestral orchid forms were able to conquer an almost empty habitat: the branches of the canopy. Over time, via mechanisms like the repeated fragmentation of the forest environment and co-evolution with pollinators, these ancestral forms radiated into the stunning array of orchids that we encounter today.

TEMPERATE FORESTS OF AUSTRALIA

The dry forests and woodlands of Western Australia harbor a rich diversity of terrestrial orchids. Many of these eucalyptus-dominated forests frequently experience fires that clear out the undergrowth and create ideal conditions for orchids to be found by their pollinators.

EXTREME TROPICAL HABITATS

Along Caribbean coastlines, mangrove forests often define the transition from ocean to land. From an orchid's perspective, these forests present a very challenging habitat because of their high salinity and radiation and their limited freshwater. Still, some epiphytic orchids have conquered this special habitat and can be quite common in mangrove stands.

KARST HABITATS

Karst landscapes are difficult habitats for all plants. The Swiss cheese–like soils, composed of limestone or old lava flows, drain extremely fast, so water from rainfall runs off rather than being absorbed. Orchids, with their adaptations to drought, are especially suited to this kind of habitat and can thrive in karst grasslands.

MACCHIA HABITAT

Winter rains and summer heat blanket some areas around the Mediterranean in southern Europe, giving rise to a challenging plant habitat called macchia. Similar to the dense, low shrublands of North American chaparral, macchia has poor, often limy soil and limited water—ideal conditions for an impressive number of orchid species.
(Continues...)

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Excerpted from DECEPTIVE BEAUTIES by CHRISTIAN ZIEGLER. Copyright © 2013 by Christian Ziegler. Excerpted by permission of THE UNIVERSITY OF CHICAGO PRESS.
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