Pontederia L.
Pontederia is a small genus with six species (although many more have been described). All are native to the New World. Molecular studies demonstrated that it is monophyletic but embedded in Eichhornia (Graham & al. 1998). A single species, P. cordata, is cultivated as an ornamental submerged or marginal plant in pools and ponds and as a bog plant (Jäger & al. 2008).
Literature:
Graham S.W., Kohn J.R., Morton B.R., Eckenwalder J.E. & Barrett S.C.H. (1998) Phylogenetic congruence and discordance among one morphological and three molecular data sets from Pontederiaceae. Syst. Biol. 47: 545-567.
Horn C.N. (1991) No.498: Taxonomic problems in the genera Eichhornia and Pontederia (Pontederiaceae). Amer. J. Bot. 78 (Suppl.) 6: 192-193.
Horn C.N. (2002) Pontederiaceae. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 26. Oxford University Press, New York-Oxford: 37-46. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=10722]
Horn C.N. & Haynes R.R. (1987) Typification of Pontederia and its Linnaean species names (Pontederiaceae). Taxon 36(3): 621-625.
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Lowden R.M. (1973) A revision of the genus Pontederia L. Rhodora 75: 426-487. [available online at: https://archive.org/details/cbarchive_132004_revisionofthegenuspontederial1973]