Myriophyllum beautiful but a nuisance

Myriophyllum or Red stem is a water plant that prefers to take root on the transition from land to water. The stems can grow up to 2 meters long and protrude a few decimetres above the water. Red stem grows particularly well in shallow, warm and nutrient-rich waters. The plant usually roots in shallow riparian zones, but free-floating stems without roots can also survive in nutrient-rich deep water. Red stem is originally from South America.

Myriophyllum was imported for trade in pond and aquarium plants. The plants come into nature because people throw away excess plants in public waters, after which they can spread further.

Red stem can quickly provide a lot of biomass, which leads to dense mats floating on the water surface. As a result, native plants are displaced, underwater plants die and existing animals disappear. The death of large masses of Red stem in standing water can lead to a lack of oxygen in the water. This has a negative impact on other aquatic organisms and can lead to fish mortality.

Dense mats of Red stem obstruct the flow of water. Due to the reduced flow, more sediment is also deposited on the soil, which increases the risk of flooding. Stagnant water is created in combination with the hindrance of fish to eat mosquito larvae. This promotes mosquito pests. These effects were the reason for placing this species on the EU list. Myriophyllum has been on the EU list since August 2016 with invasive exotic species in the EU. A species that is on the EU list is banned from possession, trade, growing, transport and import. Controlling the plant entails additional costs for the community.

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