Bet that you didn’t know that pine cones can move. They move their scales to protect their seeds. When it is wet outside, the pine cone is shut tight. However, when it is dry out, it opens its scales so that its seeds can disperse out into the world. Three very old pine cones (120,00 to 15 million years old) were found intact in German coal mines. Researchers placed them in water to see if they could still move. Guess what, they can!
A pine cone has two types of woody cells that are arranged one layer on top of the other. They together to make the scales of the pine cone move. The cells in the lower layer expand 20% when wet and the upper layer’s cells barely move at all. The scales are arranged in a Fibonacci sequence and passively move according to humidity. Because of this feature, rain makes the cone scales curl up and keeps the seeds protected in the cones. When it’s dry out and the seeds have a better chance of being dispersed and surviving, the pine cone opens.
Oh, ancient cones
These three pinecones were found by German miners in the 1960s and made their way to the University of Freiburg. They belong to two different genera, Pinus (think pine trees) and Keteleeria (a rarer Asian genus). The rocks that they were found in were dated to 120,000 and 15 million years old, a very long time! It is extremely rare to find such an old, intact pinecone. Pine cones off the tree are usually decomposed quickly by insects, fungi, and microbes. For this reason, the oldest pine cone that still has been able to move was 1,300 years old.
The researchers at the University of Freiburg wanted to test if these ancient pine cones could move their scales. To do so, they soaked the pine cones in water. For comparison’s sake, they also soaked a fresh, similarly-sized Scots pine (Pinus sylvestris) cone. The ancient cones still curled up, though only half as much as the fresh cone. They could still move! The reasons for the less pronounced movement could be that the two layers of cells became separated or the pine cones deteriorated.
Video of one of the pine cones moving in time-lapse. Video credits: Poppinga, S., et al. 2017
The researchers scanned the cones for mineralization. If they had a lot of mineralisation, then the pine cones would become fossilised and start turning to stone. Interestingly, the pine cones had very minimal mineralisation; just in some small spots. They were actually “coalified” instead of fossilised. Being preserved in coal allowed them to keep their structure and elasticity. If they were fossils, then they would be too solid.
The scales on the ancient pine cones are still are able to move passive-hydraulically after such a long time underground. I’d like to see what else on earth can still move after so long!
Journal reference: Poppinga, S., et al. “Hygroscopic motions of fossil conifer cones.” Scientific Reports 7 (2017): 40302.