This species is characterized by elliptic leaves with a notably stiff texture and the rounded to emarginate (or occasionally acute), pedicillate 4-merous flowers, white to pale yellow corollas with the tube 23--32 mm long, and somewhat short, stoutly woody capsules. Anunciação (2004) also separated this species by its secondary veins that are united into a submarginal vein; this vein is situated very close to the leaf margin and can be difficult to discern. Ferdinandusa elliptica species is similar to Ferdinandusa nitida. Anunciação (2004) studied variation in Ferdinandusa elliptica in the field and from specimens, and did not separate its var. belemnensis and she is followed here.
Ferdinandusa elliptica is also similar to Ferdinandusa loretensis, from wet forest in the Amazon basin. Both of these species were reported from Ecuador by Andersson & Taylor (1994), with Ferdinandusa elliptica represented by one specimen deposited in QCA. This species is illlustrated correctly in this treatment with the drawing based on a Braziilian specimen, but Anunciação (2004) did not report Ferdinandusa elliptica from the northwestern Amazon basin, and this single speciment from Ecuador needs re-confirmation.
These plants were treated in two species by Pohl, Fernandea elliptica and Fernandea ovalis, and those names were published simultaneously. Schumann (1889) appears to have been the first to treat these as one species, as noted by Andersson & Taylor (1994), and Schumann chose the name Ferdinandusa elliptica. Later authors have sometimes treated this combined species under the name Ferdinandusa ovalis, but Schumann's choice has priority.