Can you remember what you did yesterday? If not, you might want to take a lesson from Nasa poissoniana, a star-shaped flowering plant from the Peruvian Andes with an unusual skill set.
These plants can gymnastically wave around their stamens — the organs they use for fertilization — to maximize the distribution of their pollen. More surprisingly, a study published last month in Plant Signaling and Behavior suggests that individual plants can adjust the timing of these movements based on their previous experiences with pollinators. In other words, they remember the past, and try to repeat it.
The discovery joins others recently painting an ever-broader picture of what plants can sense, learn and do. The study, although small and preliminary, “presents a promising and intriguing new system to study plant memory,” said Peter Crisp, a plant geneticist at the University of Minnesota who was not involved.
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Nasa poissoniana belongs to a subfamily of plants called Loasoideae. They’re known for their polychrome blooms, as well as for the “really painful” stinging hairs on their stems, says Tilo Henning, one of the study’s lead authors.
Dr. Henning, a researcher at the Botanic Garden and Botanical Museum in Berlin, has been working with Loasoideae for nearly two decades, along with his collaborator Maximilian Weigend of the University of Bonn in Germany. From the start, “the complexity of the flowers thrilled us,” he said. So did their tendency toward thigmonasty, or triggered movement.
While other plants may curl their leaves or catapult their seeds, many species of Loasoideae move their stamens: long, skinny filaments that are capped with pollen. Loasoideae stamens start out splayed, bunched up in groups and tucked within the flower’s petals. Over the course of the flower’s life, the individual stamens swing one by one into the center of the flower, where they stand tall and offer fresh pollen to insect visitors.
It takes less than three minutes for a Loasoideae stamen to travel from the outside in — nimble by plant standards. In certain species, this movement can be provoked by light and temperature, or by the pollinators themselves. When a bee rummages around for nectar in the flower’s center, it triggers the next stamen to come sweeping in, ready for a new bee, or the previous bee’s return. In this way, the flowers maximize their chances of transferring pollen to many different flowers.
For this latest study, the researchers divided Nasa poissoniana into several groups. “Pollinators” — in this case, humans with probes — visited the first group every 15 minutes, rustling the flowers’ nectar-containing parts. They bothered the second group every 45 minutes. Other groups were left alone, as controls.
The next day, the researchers observed the flowers. Those that had been visited every 15 minutes planned for that timeline, swinging in new stamens faster and more often. The second group was more lackadaisical, and its fresh stamen concentration peaked at the 45-minute mark. The plants were “anticipating pollinator revisits,” said Dr. Henning, who expects that other members of Loasoideae also have this talent.
Heidi Appel, a plant behaviorist at the University of Toledo, said the study “provides another great example of how exquisitely tuned plants are to their environment.” But she stopped short of using the word “intelligent,” or other terms that might anthropomorphize plant behavior.
Whether you apply such adjectives to these plants or not, Dr. Henning says he wants to know why they try so hard.
“The tremendous overall expenditure these plants invest in” spreading their pollen around is puzzling, he said. “There are a number of similar successful plant groups. But none of them shows such an elaborate effort.”