Pontederia cordata (Pickerel Weed)

Scientific name

Pontederia cordataL.

Synonyms

Pontederia cordataLour.

Common names

Pickerel weed

Family

Pontederiaceae

Origin

Eastern North America, Central and South America.

Naturalised distribution (global)

Locations within which Pontederia cordata is naturalised include parts of Australia, Europe, Africa and western North America.

Introduced, naturalised or invasive in East Africa

Pontederia cordata is invasive in Kenya and is present in Tanzania and Uganda (A.B.R. Witt pers. obs.). It has been recorded in inland fresh water lakes and reservoirs, including artificial dams, reservoirs and in ponds around towns.

Habitat

Emergent water plant of water and riverine habitats.

Description

Pontederia cordata is a long-lived (perennial), rooted freshwater plant 1-2 m tall that grows in clusters and forms colonies.

The stems are smooth, emerging above the water surface and branched, each bearing a leaf and a flower spike. The leaves are light or yellowish green, cordate in shape, 230 mm long by 70 mm wide. Leaves appear one per stem each with a long petiole that clasps the stem.

The flowers of P. cordata are blue in colour and appear at the terminal end of the stem. The flowers are on long spikes 50-150 mm long. Each flower is 15 mm long and the upper petal has a yellow blotch in the centre. This plant is sterile and does not produce fruits and seed.

Reproduction and dispersal

This plant spreads vegetatively from fragmented rhizomes.

Similar species

Pontederia cordata has sometimes been confused with Eichhornia crassipes (water hyacinth another introduced water weed of the same family. These species can be readily distinguished by the following differences:

  • E. crassipes is usually a free-floating plant with leaves on or above the water surface. These leaves have a thickened, spongy, stalk (petiole) and a broad leaf blade with entire margins. Its very showy flowers (4-6 cm across) are blue, purplish or mauve in colour (with a yellowish spot).
  • P. cordata is rooted to the substrate with leaves above and below the water surface. These leaves are borne on long stalks (petioles) and have a broad to elongated leaf blade with entire margins. Its relatively small flowers (about 2 cm across) are usually blue to violet in colour, occasionally white, (with two yellowish spots).
  • E. crassipes has also sometimes been confused with Pistia stratiotes (water lettuce) when not in flower. P. stratiotes can be readily distinguished from E. crassipes by the covering of soft velvety hairs on its leaves.

Economic and other uses

Pontederia cordata is an ornamental plant. However, this use cannot compensate for this plant's overall negative impacts.

Environmental and other impacts

Pontederia cordata is a competitive weed of the inland waters and artificial ponds and water masses. It has been listed as a Category 3 invader in South Africa (no further planting is allowed - except with special permission - nor is trade in propagative material. Existing plants must be prevented from spreading).

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.

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.

The editors did not find any specific information on the management of this species.

Legislation

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

References

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.

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: eafrinet@africaonline.co.ke