This very beautiful flowering delicate plant is called bladderwort or Utricularia. It is an unusual plant on the large species list for biological pools.
A floating plant that never has roots is usually not very suitable for use in a biological pool because it could appear in the bathing area. But in certain biological pool configurations it could be used, for example, when the plant zone is separated from the bathing zone.
In addition to the yellow flower with red dots Utricularia has a special feature, this aquatic catches and eats aquatic insects. To achieve this, the plant has real underwater “traps” in the leaves. The second picture shows these green structures in the form of a small bean, very small, no larger than one millimeter. Inside is a vacuum and if an animal passes by and touches the small lashes on the outside of this trap, it will open very fast, that is, it opens and the vacuum causes the animal to be swallowed in the bubble where it is digested in the following hours.
There are three bladderwort species in the Portuguese flora of which one is considered extinct. The other two are rare. The biological swimming pool nursery reproduces one of them shown in the pictures.