This species is commonly collected, at least in western Amazonia. It is similar in general aspect to Ladenbergia oblongifolia, but differs from that species in its rather congested inflorescences, leaves apparently without domatia, and somewhat larger corollas, with the tube 13-16 mm long, vs. lax inflorescences, leaves with well developed pilosulous domatia, and corolla tubes 6-14 mm long in L. oblongifolia. Andersson (1997) distinguished these species in part by their flowers, with the corolla papillose inside above the stamen attachment and the style glabrous or more often pubescent in L. amazonensis, vs. the corolla smooth inside and the style always glabrous in L. oblongifolia.

Several similar Ladenbergia species are also found in the Amazon lowlands: L. graciliflora has short calyx limbs, 1-1.5 mm long, and longer corollas than L. amazonensis; L. lambertiana has generally narrower leaves and slender capsules; Ladenbergia pittieri has calyx limbs ca. 3 mm long and corollas similar in size to L. graciliflora; and L. paraensis has a subtruncate calyx limb, corollas with the tube ca. 18 mm long, and is known only from a single collection from Para in northeastern Brazil.