EPPO Alert List – Myriophyllum rubricaule (Haloragaceae)

Why

Myriophyllum rubricaule (Haloragaceae) is a recently described species with a limited distribution in the EPPO region. The EPPO Panel on Invasive Alien Plants are seeking further information on any additional occurrences of M. rubricaule in the EPPO region and reports of environmental and economic impacts.

Geographical distribution

EPPO region: Belgium, Hungary, Netherlands.

South America: Chile (native).

Courtesy: Johan van Valkenburg

Morphology

Myriophyllum rubricaule is an amphibious or aquatic species, only known from female plants in the introduced range. Stems are unbranched or with up to 6 branches per 20 cm, often rooting at submerged and lower emerged nodes. Leaves in whorls of 4 or 5, opposite and/or alternate. Submerged leaves are olive green or turning pale to dark reddish brown. Emerged leaves are bright green to bluish green, sometimes tinged red brown or pinnae red-tipped. Flowers solitary in the axils of the emerged leaves, tinged pink. Fruits have not been observed.

Biology and Ecology

No seed production has been observed in the EPPO region and it is likely that dispersal is via regeneration of plants/stem fragments. It is likely that M. rubricaule will be able to grow in a wide range of physical and chemical conditions. Survival in an open air pond under Dutch winter conditions has been observed for over 10 years.

Habitats

Slow moving water bodies including rivers, irrigation channels, ponds, lakes, canals and damp ditches.

Pathways for movement

Aquarium and horticultural trade. M. rubricaule is known to have escaped from cultivation in the EPPO region. The species can appear in trade incorrectly labelled often as Myriophyllum brasiliensis or M. brasiliense. Entry into the natural environment is potentially via the dumping of aquarium or garden waste.

Impacts

Potential impacts are likely to be similar to that of M. aquaticum, although the plant is of more modest dimensions. Dense mats of M. rubricaule could block sunlight which may alter the quality of the water body by reducing oxygen levels. This can have a negative impact on invertebrates and plant species in the invaded habitat. Ecosystem services can be negatively affected, for example by reducing access to the water body or blocking irrigation channels.

Control

Control methods would be similar to other non-native Myriophyllum species. Chemical control methods are largely not applied on or near water bodies in Europe. Mechanical control can be attempted though it is difficult to remove all material from a waterbody.

Sources

Van Valkenburg JLCH, Duistermaat L, Boer E, Raaymakers TM (2022) Myriophyllum rubricaule sp. nov., a M. aquaticum look-alike only known in cultivation. European Journal of Taxonomy 828, 1–15. https://doi.org/10.5852/ejt.2022.828.1847

Van Valkenburg JLCH, Boer E (2015) Cabomba and Myriophyllum in trade, What’s in a name? In: Newman J. (ed.) Abstracts 47^th Robson meeting, Reading, England: 16–17, Waterland management, United Kingdom.

Van Valkenburg J, Duistermaat L, Westenberg M, van de Vossenberg B (2015) Myriophyllum in trade in Western Europe, what species are we really talking about? In: Aquatic Plants 2015, 14^th International Symposium on Aquatic Plants, p 57. The Centre for Ecology & Hydrology, Edinburgh, United Kingdom.