In the sun-drenched mountains of southern Spain, one type of thistle seems to have built-in air conditioning.
The flowers of this plant — Carlina corymbose — stay cooler than the hot air around them. Ecologist Carlos Herrera reports they are, on average, about 3 degrees Celsius (5.4 degrees Fahrenheit) cooler. But during the hottest part of the day, the temperature difference becomes even more extreme. The flowers can cool up to 10 degrees Celsius (18 degrees Fahrenheit).
So, when the air reaches a blazing 45 °C (113 °F), the plant’s flowers can remain a relatively chilled 35 °C (95 °F). Herrera shared his findings February 13 in Ecology.
“Those are substantial coolings relative to the air next to it,” says ecologist Christopher Still. He works at Oregon State University in Corvallis. He was not involved in the work, but says, “It’s a nice, careful study.”
A chance discovery
In Spain’s Sierra de Cazorla mountain range, scorching summers leave many plants dead, dried out or dormant. But in this brown sea, bursts of yellow thistle flowers peek above browned-out neighbors.
On a recent trek through the mountains, Herrera touched one of the thistle heads. Even though it was the peak of the day’s heat, the bloom felt pleasantly cool.
Herrera works at the Spanish National Research Council in Sevilla. But he was up in the mountains to study links between the region’s plants and their pollinators. He recalls bending over to touch the bloom because he “was checking for the presence of nectar in the flower head.”
But once he did, he became curious about why the flower felt chilled. He decided to find out more.
Using an electric thermometer, he measured the temperatures of seven thistles across two different sites. Herrera checked each bloom many times and on different days. The flowers grew consistently cooler as the day heated up.
Many plants beat the heat by letting water evaporate through tiny holes, or…
Read the full article here