You may have heard of jewelweed. It has seed pods that spring open when you touch them, allowing you to eat the delicious, nutty seeds, and is an excellent antidote for poison ivy. I bet you didn’t know this, though. Jewelweed can tell its “siblings” from “strangers.” By “siblings,” I mean other plants which originated from seeds from the same plant.
In an experiment, scientists placed jewelweed in pots with strangers, with siblings, and alone. (Pictured below.) Those plants growing with their siblings grew slightly differently than the ones alone, putting out more branches. Those growing with strangers, however, engaged in utter leaf warfare, each putting all their spare energy into growing leaves and, hopefully, getting more sunlight than the other plant. Scientists also found that strangers would not react to each other if they were in different pots, no matter how close they were. This led them to believe that the plants identified each other through their roots. Why do the plants do this? We don’t really know, but one theory is that sibling recognition is a by-product of self-recognition.