Scientific name

Myriophyllum aquaticum (Vell.) Verdc.

Synonyms

Enydria aquatica (Vell.) Verdc.; Myriophyllum brasiliense (Cam.); Myriophyllum proserpinacoides (Gillies ex Hook. & Arn.)

Common names

Water feather, parrot's feather, Brazilian water-milfoil

Family

Haloragaceae

Origin

Myriophyllum aquaticum is native to South America

Naturalised distribution (global)

Locations within which Myriophyllum aquaticum is naturalised include Australia, southern and eastern Africa, warm and cool temperate Europe and some islands in tropical and temperate parts of the world.

Introduced, naturalised or invasive in East Africa

Myriophyllum aquaticum is invasive in Kenya and Tanzania. It  has been recorded in parts of Nairobi and Central province in Kenya, and in North eastern Tanzania.

Habitat

Myriophyllum aquaticum occurs in freshwater lakes, ponds, streams and canals. It has been found to thrive in  well lit, high nutrient waters.

Description

Myriophyllum aquaticum is a long-lived (perennial)  herbaceous plant that grows submerged or emergent in fresh water habitats.

The submerged leaves of M. aquaticum measure1.5-3.5 cm long and have 20-30 divisions per leaf. The emergent leaves measure 2-5 cm long and have 6-18 divisions per leaf. The bright green emergent leaves are stiffer and a darker green than the submersed leaves. Submerged leaves are limp and often appear to be decaying but stems are very robust, with adventitious roots forming at the nodes.

Flowers of M. aquaticum are white, inconspicuous and form where emergent leaves attach to the stem.

Reproduction and dispersal

Myriophyllum aquaticum spreads by fragments and often by intentional plantings. With its tough rhizomes, M. aquaticum can be transported long distances on boat trailers and can root after many months.  Male plants are unknown outside of South America so no seeds are produced outside its native range.

Economic and other uses

Myriophyllum aquaticum has been introduced worldwide for use in indoor and outdoor aquaria. It is also a popular aquatic garden plant. However, these uses cannot compensate for this plant's overall negative impacts.

Environmental and other impacts

Myriophyllum aquaticum can rapidly colonise wetlands and forms dense mats that obstruct boat passage, trap sediments and crowd out native vegetation. Light is strongly reduced and water flow impeded  (Weber, 2003).

M. aquaticum has been included in the Global Invasive Species Database (GISD 2005). It has been listed as a noxious weed in South Africa (prohibited plants that must be controlled. They serve no economic purpose and possess characteristics that are harmful to humans, animals or the environment) and in several Australian states.

Management

The precise management measures adopted for any plant invasion will depend upon factors such as the terrain, the cost and availability of labour, the severity of the infestation and the presence of other invasive species. Some components of an integrated management approach are introduced below.

The best form of invasive species management is prevention. If prevention is no longer possible, it is best to treat the weed infestations when they are small to prevent them from establishing (early detection and rapid response). Control is generally best applied to the least infested areas before dense infestations are tackled. Consistent follow-up work is required for sustainable management.

Although Myriophyllum aquaticum is considered by some to be susceptible to herbicides, it is difficult to achieve complete control since the emergent stems and leaves have a thick waxy cuticle that requires a wetting agent to penetrate.

Use of mechanical controls such as cutting, harvesting, and rotovation (underwater rototilling) while the plant is still invading is discouraged since they tend to enhance its rate of spread. Mechanical controls should be used only when the extent of the infestation is such that all available niches have been filled.

Biological control using an insect species of the genus Lysathia is proving to be effective in South Africa.

Legislation

Not listed as a noxious weed by the state or governments in Kenya, Tanzania and Uganda.

Notes

Myriophyllum aquaticum derives its name from the fact that its leaves are feather-like and are arranged around the stem in whorls of four to six.

References

GISD (2005). Global Invasive Species Database online data sheet. Myriophyllum aquaticum (aquatic plant). www.issg.org/database. Accessed March 2011.

Henderson, L. (2001).  Alien weeds and invasive plants. A complete guide to declared weeds and invaders in South Africa.  Plant Protection Research Institute Handbook No. 12, 300pp. PPR, ARC South Africa.

Henderson, L. and Cilliers, C.J. 2002. Invasive aquatic plants-a guide to the identification of the most important and potentially dangerous invasive aquatic and wetland plants in South Africa. PPRI Handbook No. 16, Agricultural Research Council, Pretoria.www.arc.agric.za/uploads/images/0_SAPIA_NEWS_No._17.pdf.

Weber E. (2003). Invasive Plant Species of the World. A Reference Guide to Environmental Weeds. Wallingford, UK: CABI Publishing.

Editors

Agnes Lusweti, National Museums of Kenya; Emily Wabuyele, National Museums of Kenya, Paul Ssegawa, Makerere University; John Mauremootoo, BioNET-INTERNATIONAL Secretariat - UK.

Acknowledgments

This fact sheet is adapted from The Environmental Weeds of Australia by Sheldon Navie and Steve Adkins, Centre for Biological Information Technology, University of Queensland. We recognise the support from the National Museums of Kenya, Tropical Pesticides Research Institute (TPRI) - Tanzania and Makerere University, Uganda. This activity was undertaken as part of the BioNET-EAFRINET UVIMA Project (Taxonomy for Development in East Africa).

Contact

BioNET-EAFRINET Regional Coordinator: [email protected]