Araucaria columnaris, also known as the coral reef araucaria, Cook pine or New Caledonia pine, is a species of conifer native to New Caledonia that tends to tilt sideways when planted outside its natural habitat.

First classified by Johann Reinhold Forster, a botanist accompanying Captain James Cook on his second voyage to circumnavigate the globe as far south as possible, the araucaria columnaris soon became popular all around the world, thanks to its distinctive narrowly conical shape and its height (up to 60 meters). Nowadays, these evergreen giants are planted as ornamental trees in various areas with warm and temperate climate on five continents, and they generally don’t attract too much attention, but in some cases they have one noticeable particularity – they lean heavily to one side, and when there are more of them planted in the same area, they all lean in the same direction…

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Under most conditions, trees tend to grow vertically, with one known exception being challenging environments, where competition for light or nutrients and mechanical stress can cause trees to crow crookedly. However, that didn’t seem to be the case with araucaria columnaris, as their leaning tendency was noticed even very favorable environments.

Scientists were puzzled by the growth of araucaria columnaris trees for years, but no one had a plausible explanation. American botanist Matt Ritter set out to find out the cause of the unusual phenomenon and started documenting the growth of Cook pines in North America. He noticed that all the observed specimens leaned their tops towards the south, and shared his findings with a friend and colleague from Australia, who told him that where he was, all the New Caledonia pine trees seemed to lean north.

Intrigued by their findings, Ritter and a number of colleagues traveled the world looking for araucaria columnaris trees and documented their leaning tendencies. After examining 265 leaning specimens, the scientists concluded that the Cook pines’ lean is non-random: trees in the northern hemisphere lean south, and those in the southern hemisphere lean north.

“Additionally, the magnitude of the lean is more pronounced at higher latitudes in both hemispheres. Our data and the pattern that we describe here elucidate the fact that plants are responding to their global environment in a way not yet fully understood,” the scientists noted in a paper published in 2017.

In the southern hemisphere, the trees bent to the north, while in the Northern they bent to the south, and only around the equator did they grow almost vertically. Moreover, the angle of inclination of the araucaria columnaris was directly related to the distance from the equator. The further from the equator, the stronger their bend.

The cause of directional lean in this species is unclear, but Ritter and his colleagues hypothesize that it “may be related to an adaptive tropic response to the incidence angles of annual sunlight, gravity, magnetism, or any combination of these”.

Interestingly, the pronounced lean in Araucaria columnaris trees is rare in other species, including other Araucaria native to New Caledonia.