Urban heat is driving explosive evolution in a wild plant

Urban growth usually squeezes nature into ever-smaller fragments. But it also creates a patchwork of microhabitats, including hot pavements, shaded parks, and compacted soils, that can push wild plant species to adapt quickly.

A Kobe University team reports that a native plant thriving from rice paddies to roadside cracks has split into distinct, inheritable forms across the Osaka-Kyoto-Kobe “Keihanshin” megacity, revealing rapid urban evolution in action.

One plant, many urban forms

The star of the study is the Asiatic dayflower (Commelina communis), a hardy annual whose blue blooms pop up from fields to footpaths.

Ecologist Atsushi Ushimaru has tracked the species for more than two decades and noticed how vigorously it colonizes built environments.

His former graduate student – now Kyushu University researcher – Taichi Nakata, saw something that didn’t fit the usual rural-vs-urban story.

“While observing the plant in different urban environments, I noticed differences in size, flowers, and flowering periods, which got me curious as to what causes these variations,” said Nakata.

Rather than lumping “the city” into a single category, the team investigated how different urban habitats – such as parks, roadsides, or pavement seams – compare with relatively intact farmlands still threaded through the Keihanshin sprawl. The geography made it possible.

“This region retains a significant amount of farmland within the urban area, providing conditions where we could compare relatively well-preserved farmlands with parks and roadsides,” Ushimaru said.

Heat and soil drive plant change

The researchers found consistent differences in traits such as plant height and flowering timing, tied to where dayflowers grew.

“We could clearly show that adaptive radiation occurred, which is what biologists call it when a species diversifies across different habitats,” Ushimaru said. “And we found that factors clearly associated with urbanization.”

The clearest driver was heat. On average, maximum ground temperatures in urban sites ran about 14°F (8°C) hotter than in the countryside, a textbook heat island effect.

That thermal load isn’t just unpleasant for humans. It reshapes plant life cycles and physiology.

Shade patterns also differ in cities, thanks to buildings, overpasses, and managed canopy. And urban soils are often less acidic, reflecting construction materials, runoff, and maintenance practices.

Together, these stressors and quirks create a mosaic of selective pressures that can nudge populations down different evolutionary paths.

Evolution moving at city speed

What makes the finding striking isn’t just the pattern but the pace. Much of the study area was rice paddies and forest less than a century ago. Intense urbanization picked up only in the last 60 years.

The team took care to rule out simple “founder effects,” where a few colonizing plants could make a patch look different by chance.

After accounting for that, they concluded the dayflower’s divergent traits are heritable and best explained by selection within living memory. As they put it, the shifts are “likely attributable to rapid adaptive evolution over only approximately 60 years.”

That speed matters. It suggests common native species can keep up with the moving target of urban conditions, sometimes by becoming many slightly different versions of themselves.

The research highlights why focusing solely on species counts can miss the story. The same species can express very different forms and functions from one city niche to the next.

New rules for city nature

The work also pushes urban ecology past the binary lens of rural versus urban. Many studies document biodiversity losses with city growth – and those losses are real. But cities aren’t uniform wastelands. They’re dynamic mosaics.

The fact that a single native plant can radiate into distinct urban types hints that conservation planning should pay attention to microhabitat diversity within towns, not just green-versus-gray maps. It’s also a reminder that cities can serve as living laboratories for evolution.

Rapid, repeatable environmental contrasts like hot asphalt, cool park understories, or altered soils let researchers test how traits track specific stressors.

Because those stressors are measurable and, in principle, manageable, the findings can loop back into design.

If extreme surface heat is driving trait shifts, urban cooling (tree cover, reflective materials, permeable pavements) might soften that selection pressure and support broader sets of species and forms.

What drives these new plant forms

The Kobe team is now moving from pattern to mechanism. “We want to conduct cultivation experiments that replicate the complex field environments to clarify how the different traits are beneficial to the plants,” Ushimaru said.

“And we also want to know to what degree these adaptations are engraved into the plants’ DNA.”

Those common-garden tests can confirm whether the observed differences boost survival or reproduction under particular urban conditions, while genetic work can pin down how deeply the changes are encoded.

For Nakata, the results open more doors than they close. “These findings are just the starting point for research on a larger scale.”

The study is published in the Journal of Ecology.

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