In the sundew Drosera spatulata, a small carnivorous plant, flowers can snap shut within minutes of being touched. This rapid movement protects the plant’s precious ovules from hungry caterpillars. Now, new research shows that damage to the leaves days earlier makes those flowers close even more tightly when danger approaches, as if the leaves are sending a warning to the flowers.
The study, researchers say, suggests that plants can use information from one part of their body to adjust defenses in another, helping them respond more effectively to threats. “Such retention and use of past information may be regarded as a kind of ‘memory,'” says the researchers.
Biologists have long known that many plants can remember past attacks and prepare stronger defenses for the future. This process, called priming, usually happens within the same organ — a damaged leaf might better protect nearby leaves. But cross-organ effects, where leaf damage influences flower behavior, have been far less studied.
Drosera spatulata plant produces sticky, insect-trapping leaves, but it also grows delicate pink flowers. A specialist caterpillar, Buckleria paludum, exploits this plant. The caterpillars begin by feeding on leaves and later move to flowers and fruits as they grow. That feeding pattern means leaf damage could serve as a reliable signal of future risk to the flowers.
Kazuki Tagawa at the Naruto University of Education in Japan and colleagues simulated this natural sequence in the lab. They collected flowering plants from a population in Naruto, Tokushima, Japan, where the specialist caterpillar had not been seen for years. This ensured that any effects came from the experimental treatment rather than prior real-world experience.
In one group of plants, the team clipped about half the area of two healthy leaves the evening before the flowers opened. A control group received no damage. The next morning, during the flowers’ normal opening period, the researchers applied a standardized mechanical stimulus to the base of the flower using forceps — mimicking the kind of contact a crawling caterpillar might make. They photographed the flowers immediately before stimulation and again at 5 and 15 minutes afterward. Using image analysis software, they measured how tightly the petals closed by recording the angle between the outermost petals and the base of the flower.
Flowers on plants that had experienced prior leaf damage closed to significantly smaller angles — indicating a stronger defensive response — compared to flowers on undamaged control plants. At five minutes, the effect was not yet statistically detectable, but by 15 minutes it was clear and robust.
The main comparison involved 15 plants with simulated leaf herbivory and 17 control plants. Statistical models confirmed the treatment effect while accounting for factors such as the time of day and the number of previously opened flowers on the stalk.
Observations of the caterpillars showed they typically take around 15 to 20 minutes to climb from the base of the flower to the more vulnerable reproductive parts after first contact. A tighter closure within that window would be especially effective at redirecting the insect away from the ovules toward less critical structures like petals.
The study also revealed an interesting interaction with the time of day. In control plants without prior damage, flowers tended to close more tightly later in the morning. This may reflect declining opportunities for pollination as the day progresses — the flowers normally close around midday on their own schedule. With fewer chances for outcrossing, the cost of a false alarm (closing unnecessarily) decreases, so the plant becomes more defensive. Plants with prior leaf damage, however, showed consistently strong closure regardless of the hour, as if the earlier damage had raised their overall assessment of risk.
“Plants must balance the risks of responding to unreliable cues with the costs of failing to defend against attack,” the researchers note in their paper. Mechanical contact can come from wind, rain, or harmless visitors, so responding to every touch would be wasteful. But failing to respond to a real herbivore could mean losing seeds.
“Such retention and use of past information may be regarded as a kind of ‘memory’,” the authors write.
The study has been published in the journal Ethology.
