http://www.aquariumfish.net/catalog_pages/plants/plants.htm
scroll down it is listed under argentine sword
Edit: this is what I found so far.
Argentine Sword Plant
Freshwater Aquarium Plant Care
Scientific Name Echinodorus argentinensis
Size Up to 18 inches
pH 6.8 - 7.5
Temperature 60°F - 77°F
Aquarium Light Needed 50 watts for every 25 gallons
Water Hardness soft-hard
Origin South America
Care Grows better in softer water than hard water. Optimal growth may not occur if the water is too hard. Plant in a loose substrate and supplement with an iron fertilizer
Edit: this is another thing I found about it.
« Echinodorus angustifoliusEchinodorus aschersonianus »Echinodorus argentinensis
by SarahFish
Its synonyms are: E. grandiflrus ovatus Mich.; E. ellipticus var. latifolius Micheli sensu Hauman; Alisma grandiflora; E. longistylus hort.
Emerse leaves erect, long-petioled, 80 - 120 cm long. Blade ovate, at the tip shortly acuminate, at the base abrupt, or regularly oval, at the tip blunt or incised, 15 - 26 cm x 7 - 15 cm wide with 7 - 13 veins and distinct pellucid lines. Submersed leaves on short petioles, blades oval or ovate, on both ends acuminate or blunt. This species has two forms.
Stem erect, 90 - 150 cm long, sparse and inconspicuously warted, infloresence paniculate, broadly branched in the lower whorl, having 5 - 12 whorls containing 6 - 12 flowers each. Bracts shorter or longer than the pedicels. Pedicels 1 - 2.5 cm long, sepals broadly ovate, ribbed, 4 - 6 mm long, petals white, corolla 3 - 4 cm in diameter. Stamens usually 24. Aggregate fruit globular, shortly echinate, achenes compressed, 3 mm long x 1 mm wide, having 3 - 5 ribs and 3 glands placed usually in one row, beak 0.4 - 0.5 mm long.
Veins are often dark reddish-brown ansd the blade may have reddish-brown irregular spots.
Needs a deep rich substrate and good light. Will withstand sub-tropical - tropical temperatures. A strong grower, too big for the average aquarium, the leaves soon growing out of the water. In the wild it grows in sticky mud along rivers. Rataj reports hybrids with E. grandiflorus and E. longiscapus which have mixed features. Supplement with iron and CO2 if possible. Seems to prefer soft to hard water.
Seems to bloom best in cooler water and in short-day conditions.
Apparently rarely found in the trade, the majority (if not all) specimens being offered being E. palaefolius.
Edit:
http://www.birstall.co.uk/cgi-bin/Shop.cgi?Store=www.birstall.co.uk&Action=aquariumplants.htm