Pontederia cordata

Taxonomy 

Pontederia cordata L., Pickerelweed, has various synonyms:

  • Narukila cordata (L.) Nieuwl.
  • Pontederia angustifolia Pursh.
  • P. sagittata C.Presl.
  • P. lancifolia Muhl. Nutt.

It is the only member of the Pontederiaceae likely to be found growing in the wild in Britain. Other members of this small family are not hardy enough to survive the winter. One other species from this family, the Water hyacinth (Eichhornia crassipes), is occasionally cultivated in gardens. The Pontederiaceae are in the order Commelinales of the monocots.

Chromosome No.: 2n = 16 (Stace 2010).

Pontederia cordata

Photography: A.J.Lockton

Identification 

It is a rhizomatous, perennial aquatic. It has two kinds of leaves, submerged, sessile leaves with linear blades, and either emerging or floating leaves with lanceolate to cordate blades. The emerging leaves are 10-20 cm across bright glossy green on long fleshy petioles. It flowers during the summer, with showy spikes of 100 or more violet-blue flowers held well above the leaves. Each flower is about 2-3 cm across and zygomorphic.

Pontederia cordata

Photography: A.J. Lockton

Distribution 

It is native in North and South America, from Canada to Argentina. However, it has naturalised widely outside its native range and is officially a noxious weed in Australia and South Africa. In Britain it was first recorded in Wimborne, Dorset in 1949, though the Flora of Dorset states ‘rarely surviving for long,’ perhaps implying that this site has now gone. Records exist for England, Scotland, Wales and Ireland, but it is most often found along the south-coast of England, particularly in Surrey and Sussex.

BSBI Hectad Map 

Click on the map to view full-size on the BSBI Maps Scheme website.

Status 
  • Origin: not native in Britain.
  • Rarity: not rare.
  • Threat: it appears to be increasing, but this is likely to be because of deliberate introductions, rather than to a natural spread.
  • Conservation: like many non-native plants, it is sometimes considered a threat to biodiversity, and is eradicated; but there is no real evidence for any damage.
Further Work 

Nothing appears to be known of which of the many described varieties from the New World grow in the Great Britain and Ireland.

Can all of the three of the tristylous morphs be found?

Is Pontederia cordata hardy enough to survive the hardest winters?

References 
  • Horn, C.N. & Haynes, R.R. 1987. Typification of Pontederia and its Linnaean species names (Pontederiaceae). Taxon 36 (3), 621-625. eFloras (2008). Published on the Internet http://www.efloras.org [accessed 27 April 2008] Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.
Citation 
Groom, Q.J. (date accessed). Species account: Pontederia cordata. Botanical Society of the British Isles, www.bsbi.org.uk.

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