The lower leaves of a teasel grow opposite each other in pairs and each pair joins together around the stem, forming a cup. The cups fill with rainwater and insects fall into the little pools where they drown.
Some plants do set deliberate traps for insects. In 2011 researchers conducted an experiment to find out if the insects that drown in the cups formed by the teasel’s perfoliate leaves are just unhappy accidents or if they contribute to the plant’s nutrition in the same way as do the insects trapped by plants we know to be carnivorous.
A control group of plants were set up in which the little cups around the stem were allowed to fill with rainwater but insects were prevented from falling in. The experimental group of plants were fed precise numbers of insects.
The experimental group did not grow significantly taller or larger than the control group but they made seed significantly earlier. The researchers came to the conclusion that the insects added, in some undefined way, to the diet of the plants in that group.
Botanists are reluctant to call teasels carnivorous because carnivorous plants such as pitcher plants or sundew secrete digestive juices into their insect traps and teasels do not do this. The insects in a teasel’s trap just disintegrate in the water that drowned them and the plant must take in some kind of nutrition from the insect soup through its leaves or its stems.
Our park is full of the most extraordinary inter-relationships between species.
Pitcher plant and sundew