This species is circumscribed more narrowly here than by previous authors. It is characterized by a lianescent to arching or erect shrub habit, well developed peduncles, congested to rather lax dichasial inflorescences with narrowly triangular to linear, often deciduous bracts 1-5 mm long, calyx limbs 1-2 mm long, corollas with the tube 11-25 mm long and lobes 3-7 mm long, fruits 18-20 x 9-10  mm, and a habitat in wet Amazonian lowland vegetation. 

Guettarda grandiflora has long been included in the circumsription of Guettarda aromatica, but these are separated here. Guettarda aromatica is characterized by subcapitate inflorescences, regularly well developed, broadly triangular to ovate bracts, and a habitat usualy in wet, seasonally inundated vegetation. Guettarda grandiflora is much more commonly collected. These have been combined in the central and western Amazon basin for some time (e.g., Klug 3946, a specimen of Guettarda grandiflora but identified as Guettarda aromatica by Standley in the 1930's; Steyermark, 1972: 366).  

Guettarda grandiflora is similar to Guettarda pohliana, which is found widely across the central to eastern Brazil and eastern Bolivia in seasonal to dfy, forest and cerrado wet forest and has calyx limbs 2.5-4.5 mm long. These have been previously treated as two species, but Guettarda grandiflora was included by those authors in Guettarda aromatica, and the separation between Guettarda pohliana and Guettarda grandiflora was based on different characters. Guettarda pohliana and Guettarda grandiflora are separated here by the calyx and habitat characters noted here. Both of these last two species have corollas that vary markedly in length, perhaps due to habitat differences and specimen preparation. A few specimens from 1700-2000 m in southern Peru are equivocal, with the short calyx of Guettarda grandiflora but the dry habitat of Guettarda pholiana.

Guettarda grandiflora is also similar to Guettarda ferox, and the overall systematics and circumscription of Guettarda grandfiflora including its  its separation from Guettarda ferox deserve further study.