Myriophyllum heterophyllum

Myriophyllum heterophyllum, the variable-leaved milfoil, originates from eastern North America, where it colonises lakes, ponds, rivers and streams. It has, however, spread as an invasive species to other parts of North America and also occurs as an introduced plant in Europe (including Germany).

This aquatic plant forms both underwater shoots with finely pinnate leaves and flowering shoots projecting out of the water with undivided, toothed leaves. The species was named after this (heterophyllum = "variable-leaved"), but other Myriophyllum species also have different leaf forms on the same plant.

This milfoil is closely related to several other North American species such as Myriophyllum hippuroides, M. pinnatum and M. laxum, which it also closely resembles. In the underwater form these species cannot be reliably distinguished from one another. In North America, hybrids of M. heterophyllum with M. laxum and M. hippuroides have also been demonstrated.

As already mentioned, the variable-leaved milfoil occurs naturalised in Europe (as a neophyte). In Germany it has been recorded mainly in Saxony and in the south of Brandenburg. This species probably reached European fresh waters as an aquarium or garden pond plant.

In the aquarium hobby, however, this milfoil is little known, at least by name. The name Myriophyllum heterophyllum is also hardly used in the trade. However, plants traded as "Myriophyllum pinnatum" and "M. scabratum" (a synonym of M. pinnatum) have been identified as M. heterophyllum. It should be checked at some point whether the species M. pinnatum is available in the trade at all or whether it is always wrongly labelled M. heterophyllum.

So that the variable-leaved milfoil and other non-native species do not spread further in the wild, aquatic plants from aquariums and garden ponds should never be "disposed of" in open waters or deliberately introduced there.

According to Mühlberg (1980), the keeping and propagation of M. heterophyllum corresponds to that of Myriophyllum spicatum (spiked water-milfoil), i.e. it is suitable for cold-water aquariums and ponds. We know of no concrete experience reports on M. heterophyllum. But it is possible that the variable-leaved milfoil is a common aquarium plant that also grows in warm-water tanks and is merely mostly misnamed and therefore not recognised as M. heterophyllum.

- To be continued -