Cook pines have always been known to grow at peculiar angles and scientists have finally discovered why – it is because they always tilt towards the equator.
On average these trees – which are native to New Caledonia – tilt by 8.55 degrees, which is twice as much as the Leaning Tower of Pisa.
The further the trees are from the equator the more they tilt – and researchers even found one tree in South Australia which slants at 40 degrees.
Now researchers say the strange tilt is an adaptation that helps them catch more sunlight at higher latitudes.
Scientists from California Polytechnic State University in San Luis Obispo studied 256 Cook pines, Araucaria columnaris, in five continents.
They looked at trees in 18 locations between 7 and and 35° north, and 12 and 42° south and found all trees in the northern hemisphere lean south and those in the southern hemisphere lean north.
‘It’s a shockingly distinct pattern,’ lead researcher Matt Ritter told New Scientist.
‘We got holy-smoked that there’s possibly a tree that’s leaning toward the equator wherever it grows’, he said.
Cook pines grow up to 197 feet (60 metres) tall and are characterised by their short branches.
Most trees are able to correct asymmetrical growth which means they always grow upwards but the Cook pine is an exception to the rule.
‘We could be just dealing with an artefact of its genetics that we are seeing now when we have spread it all over the world,’ he said.
It could also be an adaptation that allows the tree to catch more sunlight, Dr Ritter said.
However, scientists believe that gravity and the Earth’s magnetic field play a role in this slanted growth too.
‘When grown outside of its native range, this species has a pronounced lean so ubiquitous that it is often used as the identifying characteristic for the species’, researchers wrote in their paper, published in Ecology.
‘The mechanisms underlying directional lean of A. columnaris may be related to an adaptive tropic response to the incidence angles of annual sunlight, gravity, magnetism, or any combination of these’, they wrote.
Previous research suggests plants have a light-receptor called cryptochrome, which is activated by light and sensitive to magnetic fields.
Researchers believe being sensitive to magnetic fields helps plants react to elements in the soil which are affected by magnetism, such as calcium.
Many plants are able to lean towards a source of light when it is not directly above – a characteristic known as phototropism.
However, normally trees detect gravity and so their roots and shoots realign to point towards and away from the ground.
This means that as a tree matures it grows directly upwards unless there is some environmental factor preventing this happening – such as strong winds.
Talking about the strange case of the Cook pine, Steven Warren of the US Forest Service in Utah said, ‘this is the first time I have heard of a tree doing this’.