Cacti, often seen as slow-growing desert survivors, may actually be among the fastest-evolving plant groups on Earth, according to new research that challenges long-standing ideas about how plant species form.
A study by scientists at the University of Reading, published in Biology Letters, reveals that cacti rapidly generate new species not because of their flower size or specialised pollinators, but due to how quickly their flowers change shape over time.
Biologists have traditionally believed that specialised flowers and pollinators, an idea dating back to Charles Darwin’s work on orchids, play the key role in driving plant evolution. However, the new findings suggest a different mechanism at work in cacti.
Researchers analysed flower length data from more than 750 cactus species, spanning a vast size range from just 2 millimetres to 37 centimetres. Surprisingly, they found almost no link between flower size and how quickly new species emerged.
Instead, the study identified a strong connection between the rate of floral change and speciation. Species whose flowers evolved more rapidly were significantly more likely to split into new species, both in recent times and across deep evolutionary history.
“People may think of cacti as tough, slow-growing plants, but our research shows that the cactus family is one of the fastest-evolving plant groups on Earth,” said lead author Jamie Thompson. “What matters is how quickly flowers change shape, not how large or specialised they are.”
The findings also reshape understanding of desert ecosystems. Rather than being static and unchanging, deserts may be centres of rapid evolutionary activity, with cacti diversifying over the past 20 to 35 million years into nearly 1,850 species across the Americas.
Beyond theory, the research carries important implications for conservation. Nearly one-third of cactus species are currently threatened with extinction. Scientists say focusing on how quickly species evolve, rather than just physical traits, could help identify which are most at risk.
The study was supported by a new global database, CactEcoDB, which compiles seven years of data on cactus traits, habitats, and evolutionary relationships.
Researchers hope it will provide a crucial tool for understanding how these iconic plants may respond to accelerating climate change.
The discovery points to a broader shift in evolutionary biology: that speed of change, not just form, may hold the key to how life diversifies.
