Cacti are surprisingly fragile – and five other intriguing facts about these spiky wonders

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Date: 2024-11-12 14:31

Author: Jamie Thompson, Lecturer in Evolutionary Biology, University of Reading

Original article: https://theconversation.com/cacti-are-surprisingly-fragile-and-five-other-intriguing-facts-about-these-spiky-wonders-243218

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Few plant families are as iconic as the resilient, spiky cactus, thriving in the driest deserts and as well as decorating our offices and homes. Their success in both environments comes down to extreme adaptations for surviving with little water – whether braving the brutal sun or enduring weeks of neglect from busy “plant parents”. But there’s much more to the around 1,850 cacti species than their ruggedness. Here are six surprising facts about this succulent plant family that you may not know.

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Many people think of plants as nice-looking greens. Essential for clean air, yes, but simple organisms. A step change in research is shaking up the way scientists think about plants: they are far more complex and more like us than you might imagine. This blossoming field of science is too delightful to do it justice in one or two stories.

This article is part of a series, Plant Curious, exploring scientific studies that challenge the way you view plantlife.

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1. Cacti are no loners

Cacti are often depicted as desert loners, but are in fact deeply connected to their ecosystem. Even the formidable Sonoran saguaros that tower 40ft above the desert sand depend on “nurse plants” when young, which shelter seedlings from harsh conditions. When fully grown, cacti also depend on pollinators for reproduction, with different species relying on bees, birds, moths and even bats.

Meanwhile, cacti flowers, fruits and water-filled tissues provide food and hydration to desert animals. Some woodpeckers drill nest holes into cacti stems, then return the next year to live in them. Even in death, cacti serve. Their decaying stems create nutrient-rich shelters for insects and arachnids.

2. They survive in tropics and freezing mountains

With their thick and spiny exteriors, cacti appear in popular culture as the archetypal desert plant – from the backdrops in classic Westerns movies to the harsh landscapes of crime drama Breaking Bad. And certainly, arid and semi-arid environments support the greatest number of cactus species.

But some cacti are found in tropical rainforests, where they don’t tend to grow in soil, but on tree branches in the shaded and humid canopy. Others are found high in the Andes, where temperatures regularly fall below freezing, and sometimes form cushion-like structures. One unique species, the lava cactus (Brachycereus nesioticus), is found only on the Galapagos Islands. This cactus colonises dried lava flows, providing the foundation for an entire ecosystem.

3. The mysterious mistletoe cactus

All but one species of cactus are restricted to the Americas. The exception is the mistletoe cactus, Rhipsalis baccifera, which is found in the African tropics, Madagascar and Sri Lanka, where it grows drooping from other plants.

Scientists don’t know exactly how it got to these distant places. One hypothesis argues that birds transported mistletoe cactus seeds in their guts, but we don’t know which bird could have done this. Fruit-eating birds rarely fly over oceans without defecating along the way. In any case, why have no other cacti made similar crossings?

Another theory suggests the mistletoe cactus dates back to when the Americas and Africa were part of the supercontinent Gondwana. But the timing doesn’t add up, since cacti are thought to have evolved about 100 million years after Gondwana split.

Alternatively, 16th-century sailors might have transported them. But given the tight quarters and need for practical cargo, why would sailors prioritise a cactus? Perhaps simply because it’s beautiful.

4. The unexpected threat of climate change

Cacti emerged over millions of years as arid ecosystems expanded, evolving striking adaptations – including those succulent water-storing tissues and spines – that helped them survive in extreme environments. These traits have made them symbols of resilience and rugged beauty. You might therefore think a hotter, drier Earth would favour cacti, but they are more fragile than it would seem.

Many species are finely tuned to specific conditions. As climates shift, they may struggle to adapt, meaning hundreds of species are threatened in the near future. For instance, the tropical dry forests of the Chaco in Argentina, which host cactus species including Stetsonia coryne and Echinopsis terscheckii, are increasingly vulnerable to wildfires, which are exacerbated by invasive grasses and prolonged droughts.

5. Cacti are supercharged by moderate climes, not deserts

The flip side of extinction is speciation, the formation of new species. Cacti have some of the fastest rates of speciation in plants, though it varies widely within the family. One genus boasts over 100 species, whereas others have only one, such as the tiny Blossfeldia liliputiana in the Andes.

My recent research using machine learning suggested a surprising pattern: the fastest rates of speciation happen in moderate, Goldilocks climates. These places are neither too harsh nor too mild, such as having a moderate daily temperature fluctuation of about 10°C.

This discovery highlights a hidden sensitivity in cacti. Even Arizona’s mighty saguaros have struggled under recent heatwaves. As for the question of why arid and semi-arid places contain a high diversity of cacti, it may be due to their remarkable ability to exploit diverse ecological niches, such as through unique pollinator relationships.

6. Psychedelic cacti shaped ancient and modern cultures

Some cacti produce the powerful psychedelic compound mescaline, which causes vivid hallucinations and altered states of consciousness upon consumption. Andean cultures have consumed the high-elevation San Pedro cactus for mental and physical healing for thousands of years. Researchers even found traces in a mummified child victim (whose head was transformed into a “trophy head”, possibly as a spiritual sacrifice, between 450 and 100BC). Similarly, various Native American cultures have consumed the spineless peyote for millennia, and religious consumption is now protected in law.

More recently, Aldous Huxley’s 1954 book, The Doors of Perception, in which he recalls a mescaline experience, profoundly influenced the counterculture of the 1960s, even providing the name for the band The Doors.

Timothy Leary, the controversial Harvard professor fired for experimenting with psychedelics, read this book and became friendly with Huxley. Leary went on to be described by former US President Richard Nixon as “the most dangerous man in America” for his leading role in the 1960s psychedelic movement.

Today, research suggests mescaline may hold therapeutic promise. A 2021 survey of 452 people found that among those with depression, anxiety, PTSD or drug use disorder, nearly two-thirds reported improvement after taking mescaline, even without taking it for that purpose.

Far from just being desert survivors, cacti are sensitive, interconnected and downright mysterious. With many species under threat from extinction, it is crucial to protect these remarkable plants, preserving their evolutionary legacy.