In Rataj's taxonomy Echinodorus opacus is in Section Portalegrensii, Subgenus Echinodorus.
Other authorities place this species like E. portoalegrensis as a synonym of Echinodorus uruguayensis.
long-petioled, 16 to 22 cm long, petiole 10 to 15 cm long, blades shorter than the petioles, 5.5 to 7.5 cm long by 2.5 to 5.5 cm wide having 5 veins, heart-shaped, rarely lanceolate or oval, at the base usually lobate, rarely abrupt or acuminate, without pellucide markings.
Rhizome, short, upright.
Surface of the leaves is olive-green with lighter-coloured veins.
Brazil : Parana, Ponta Grossa
Paraguay: Santa Maria
Propagated by division or adventitious plantlets. Requires clear water. Can grow in tropical or rather cooler temperatures (down to about 14 °C and no higher than about 20 °C). Prefers a bright light and a rich substrate. Rather slow growing, mainly by its creeping rhizome.
Collected by Thomas Horemann. Inflorescence so far unknown. Rare in the aquarium trade.
Collected by Dierk Wanke. Upright inflorescence.