Why Is Everything an Orchid - by Sofia Quaglia | Nautilus - Environment - Evolution - Adaptation - Genetics - Bio-Diversity - Botany | 26th/10/2023 Orchids Were Darwin’s “Abominable Mystery.” They Continue Eluding Science - & Conservation Efforts to Save Them.
After investigating the origin of the species, Charles Darwin lunged into an exploration of something that seemed, by comparison, terribly minute: orchids. By 1862, he travelled the world wide & far, encountering incredible organisms like giant tortoises, seafaring iguanas & fossils of giant ground sloths. But he couldn’t stop thinking about a delicate, white star-shaped flower he’d been sent as a gift by his acquaintance James Bateman, (an English horticulturalist with a penchant for rare flora from Madagascar). The flower’s odd shape - with an extremely long nectar pouch hanging under its crown - stirred in him a deep, almost inexplicable fascination. “Orchids have interested me as much as almost anything in my life,” Darwin wrote. In their forms, he saw a vast landscape of the forces of selective evolution, a dance they played with their environment & their pollinators. “My little darlings,” as he sometimes referred to orchids, became his model for further exploring the forces he so broadly described in The Origin of Species. Just 3 years after the publication of that shattering work, he had produced his tome puzzling over the multitudinous, striking habits of orchids: On the Various Contrivances by Which British & Foreign Orchids Are Fertilised by Insects, and On the Good Effects of Intercrossing.
FORBIDDEN FLOWER: It's Illegal to Pick or Harvest Some Orchids, Like This Lady's Slipper Orchid. Orchids in the Lady Slipper Family Tend to Die When Removed From Their Natural Habitat. Photo by Dasha Artemieva / Shutterstock.
How a single family of flowers could vary so widely - from small & frilly, almost invisible to see, to large, gaudy & with a front pouch - left him baffled. He called this, & flower diversity as a whole, an “abominable mystery.” Indeed, there are upward of 28,000 orchid species world-wide & new ones cropping up every so often - at times even right under our noses. They have made their homes on all contemporary continents save for Antarctica - from the Arctic north, across the equator, reaching south through all but the tip of South America.
“I think the reason people become obsessed with them is because of that mystery: Why are there so many?” says Jamie Thompson, a life sciences researcher at the University of Bath, in the UK. Yet the scientific jury is still out - and fervently debating - how many species there are exactly, what secret makes them so brilliant at diversifying, and when & where orchids evolved in the 1st place. Getting to the bottom of these mysteries could help us better understand the evolutionary dynamism of this massive group of alluring plants, and how we might help them fend off upcoming decimation.
To search for answers, researchers have spent decades digging into the orchid’s past. For plants, fossil records are often hard to come by because soft organic matter is less likely to be preserved than, say, bones. To track when a plant 1st appeared on this planet, experts now tend to rely on phylo-genetic profiling: (They use DNA from different species to plot them onto a tree of life, and then use a statistical model to pull them back into the past & recreate their history).
When, in 2015, researchers used this technique to sequence 39 species from all major orchid groups, as well as data from some fossils, their findings suggested that orchids originated between 100 - 125 million years ago, most likely in Australia.1 Ancient orchids then spread to the tropics by making their way through Antarctica - (which was then connected & flourishing with vegetation). And since then, Southeast Asia is where most of their speciation has taken place.
Darwin Could Not Stop Thinking About a Delicate, White Star-Shaped Flower.
Or at least, this is currently the leading theory of orchid origins. It may soon be upended, though, as per new preliminary findings.2 An international research team has drafted a study using DNA from more than 1,900 orchid species & pin-pointed their origin north, in Laurasia, modern-day Europe, Asia, & North America. The majority of diversification happened just over the past 5 million years, their work suggests. Southern Meso-America, such as the lush Costa Rica & Panama, actually hosts the fastest speciation of orchids.
This paper, posted to a preprint site in September, hasn’t yet been peer-reviewed, & some outside experts don’t think this new hypothesis is any good. But Oscar Pérez-Escobar, the lead author of the study & a researcher at the Royal Botanic Gardens, Kew in the UK, doesn’t think his findings are controversial at all. “Understanding where things come from can help us understand why we have X or Y species, & why there are so many,” Pérez-Escobar says. Today, it takes a long logbook to account for orchids’ present diversity of appearances & habits. “There’s quite a number of innovations that orchids can do that other plants can’t, or not so well,” says Katharina Nargar, an orchid researcher at James Cook University, in Australia who contributed to the new study.
LEAF ME ALONE: This Orchid, Taeniophyllum Glandulosum, Never Grows Leaves. Instead, it Has Chloroplast-Containing Cortical Cells in its Roots, With Which it Meets all its Photosynthetic Needs. Its Roots are Not Buried in Soil, But Rather Wrap Around a Tree Trunk or Rock. Photo by Satyajit Dutta / Shutterstock.
The neatest & most helpful of these tricks, according to Nargar, is that more than 70 % of orchids have the ability to grow out of tree trunks & branches instead of soil (a capability known as epiphytism). It allows them to exploit new territories other plants cannot use, giving them “free rein,” says Nargar. Studies suggest that epiphytism evolved independently at least 14 times throughout the orchid family tree, & epiphytic orchids are “significantly richer in species” than terrestrial ones, write the authors of one study of their diversity. To successfully live in trees, they have developed the ability to absorb moisture from the air via a succulent spongy outer coating on their stem & leaves, as well as to use their roots directly to photo-synthesize. The Taeniophyllum orchid, for instance, doesn’t even have any leaves: it just uses its roots for all energy production from the sun.
For the species that haven’t evolved to live in trees, the other main running theory for their inexplicable ability to diversify lies in how specialized their flowers are at getting pollinated. For one, some orchid species are the ultimate swingers - they are very lenient in their sex lives & can produce fertile offspring with orchids from some other species, making them more likely to reproduce & more likely to often birth unique, new hybrid species, according to Nargar.
To ensure pollination, some orchids also strike up an evolutionary deal with local fauna: The plant evolves a flower so intricate it’s only accessible to a couple types of insects, and those insects are sure to only really ever pollinate other orchids. One of these striking examples is the Angraecum Sesquipedale, the orchid Darwin had grown obsessed with, which has evolved a 12-inch long and narrow satchel for its nectar so that only the Hawk moth, with an exceptionally long proboscis, can access it. Although Darwin had already mused on this possibility, the moth hadn’t yet been discovered, so his theory was only confirmed almost four decades later, in 1903.
Some Orchids are Very Lenient in Their Sex Lives.
In order to fine-tune their ability to accommodate just certain pollinators, orchids have also grown very meticulous about how they deliver their pollen gifts. Some orchids bundle their pollen in tailor-made, measured, sticky packages & fling them onto their preferred pollinators with precision so that no grains are wasted & lost along the way once they fly off, and they can only be dislodged once they reach their destination. This push to specialize pollen packaging according to available pollinators - maybe a moth, maybe a bee - has also pushed diversification. And it allows a mutant orchid to have a higher chance of having loads of offspring as less pollen goes to waste than with traditionally dispersed grains. The branch of the orchid family tree that has evolved this trick called “pollinia” has a higher speciation rate than orchids that have stuck with traditional pollen grains.4
I'M A BEE-LIEVER: This Orchid, Ophrys Apifera, Looks & Smells Like a Female Bee, Tricking Male Bees to Spend More Time With Them, & Become Un-Witting Pollinators. Photo - by Alberto Chiarle / Shutterstock.
To take their specialization a step further, some orchids evolved to mimic the mate of their preferred pollinator, or their favorite snack through looks, scent, & the release of special chemicals.5 Unknowing insects show up on their flower crown hoping to get lucky, get duped into picking up the flower’s pollen instead. Ophrys Apifera orchids look & smell like female bees. The Hammer Orchid eerily resembles a female wasp. The Satyrium Pumilum orchid, in South Africa, imitates the scent of dead animals to attract fruit flies, while Disa Pulchra orchids pretend to be other nectar-offering flowers, like the pink iris, to fool insects into coming looking for a sweet reward. Since bees, wasps & butterflies alike would clock the ploy if it were too common, it’s possible this has led orchids to vary in their mimetics as much as possible, spurring the birth of so many different species & tactics
These unique flower morphology strategies are “fundamental,” to diversification as per Dewi Pramanik, (Orchid morphology researcher at the Naturalis Bio-Diversity Center, in the Netherlands). One of her favorites is the Serapias Cordigera orchid, which has evolved to shape its hairy, burgundy flower like a comfortable resting place for the male Hoplitis Adunca bee, which will conveniently stop to rest there in between bouts of foraging, accidentally pollinating the flower. Dust-like seeds are also likely among the orchid’s arsenal for rapid diversification. A single orchid seed packet can contain up to 4 million seeds, sometimes as tiny as 0.05 mm in length - the smallest in the plant kingdom - meaning plenty can easily disperse with a single gust of wind. Though most of the dust seeds won’t ever germinate, this tiny seed technique does boost the odds for diversification compared to a plant with a heartier seed bulk as new plants can crop up quickly in new locations without too much energy expenditure, and rapidly adapt accordingly.
Though orchid excellence might not all be down to just tricks pulled by the plants themselves, as per Thompson - there are external factors at play, too. When he ran another phylogenetic statistical analysis on nearly 1,500 species of terrestrial orchids, his data suggested that their diversification “exploded” specifically when temperatures started dropping across the globe, somewhere around 10 million years ago.6 Global cooling is 700 times more likely to have influenced the orchid speciation rate than just time alone, Thompson says, making orchids “the best example of climate-driven speciation.”
Unfortunately, this also suggests extra trouble for the challenges orchids will face as the world warms. “I think extinction will increase, because a lot of them are cold-adapted, and we’ve seen in Europe, how hot it’s been this year,” says Thompson. Climate changes also put orchids at additional risk due to their hyper-specializing for one pollinator that might die off or be forced out of their habitat.
STAR-STRUCK: The Angraecum Sesquipedale Orchid - the Very Same Type Darwin Had Grown Obsessed With, Has Evolved a 12-Inch Long & Narrow Satchel for its Nectar So That Only the Hawk Moth, With an Exceptionally Long Proboscis, Can Access it. Photo by COULANGES / Shutterstock.
Going by their evolutionary history, orchids should continue to proliferate, and we should continue to discover new ones. “If you look at the number of orchid species described against time, it’s not really showing any evidence of leveling off,” according to Thomas Givnish, (professor of botany & environmental studies at the University of Wisconsin-Madison), who penned that seminal Australia-orchid-origin research. But human-caused climate change & other habitat destruction are spelling out a different future for many Orchid species.
Some calculations suggest that plant species are dying out at least 500 times faster than before 1900, with orchids high on the threat list. Bangladesh has lost 32 of its 188 identified orchid species since 1996; in the Czech Republic, the suitable habitat for endemic orchids has declined up to 92 percent; in Florida, the number of famed ghost orchid (the sought-after subject of The Orchid Thief) has declined by ½ ; orchids in India are blooming earlier than they should, potentially disrupting pollination. And according to a study published earlier this year, almost 280 known orchid species are in need of “immediate conservation action” but most of these still lack adequate protection.
If most of the diversity arose in the past 10 - 5 million years, the rapid loss of species we’re experiencing now might be too late to counteract, according to Pérez-Escobar. “We are kind of stuck,” he says. “If we don’t protect the orchids that we have left, the time it will take for that diversity to bounce back is millions of years.” He is on a mission to gather additional international collaboration to sample the DNA of all existing orchid species - however many they may be - as he thinks that will help him definitively plot out the plant’s evolutionary history.
The one thing experts seem to all agree on is that perhaps the best way to come up with strategies to effectively stop orchids’ decline7 - whether it’s going to be saving the habitats they reside in, focusing on the pollinators they rely on, cutting down on their illegal trade, or all of the above - is to somehow answer the big questions of the “abominable mystery”: What are the secrets to their success in speciation? Further parsing these details about orchid diversity can help conservationists home in on their rapid and wild evolutionary plasticity to, hopefully, give them a fighting chance at adapting to a rapidly changing world. After all, Darwin, himself noted that orchids had been “eminently useful” for him to learn how every little element, “even most trifling details of structure,” are somehow a result of natural selection.8 As he writes in a letter replete with exclamation points to a fellow botanist: “The beauty of the adaptations of parts seems to me unparalleled.”
Lead image: Rak ter samer / Shutterstock
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References:
1. Givnish, T.J., et al. Orchid historical biogeography, diversification, Antarctica, and the paradox of orchid dispersal. Journal of Biogeography 43, 1905-1916 (2016).
2. Perez-Escobar, O.A., et al. The origin and speciation of orchids. BioRxiv (2023).
3. Gravendeel, B., Smithson, A., Slik, G.J.W., & Schuiteman, A. Epiphytism and pollinator specialization: Drivers for orchid diversity? Philosophical Transactions of the Royal Society B 359, 1523-1535 (2004).
4. Givnish, T.J., et al. Orchid phylogenomics and multiple drivers of their extraordinary diversification. Proceedings of the Royal Society B 282, 20151553 (2015).
5. Ackerman, J.D., et al. Beyond the various contrivances by which orchids are pollinated: Global patterns in orchid pollination biology. Botanical Journal of the Linnean Society 202, 295-324 (2023).
6. Thompson, J.B., Davis, K.E., Dodd, H.O., Wills, M.A., & Priest, N.K. Speciation across the Earth driven by global cooling in terrestrial orchids. Proceedings of the National Academy of Sciences 120, e2102408120 (2023).
7. Fay, M.F. Orchid conservation: How can we meet the challenges in the twenty-first century? Botanical Studies 59, 16 (2018).
8. Darwin, C. Letter to J.D. Hooker. Darwin Correspondence Project. University of Cambridge (1862).
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Sofia Quaglia is a Free-Lance Journalist Writing About all Things Science & Nature as Well as How We Discuss Them. Her Work Has Appeared in The New York Times, BBC, National Geographic, The Guardian, New Scientist, & More. She is On a Mission to Visit the Entire Planet by Spending Each Month in a Different Country, So She has Been Living on the Road Since 2021. ______________________________________________________________________________
