This species is characterized by its medium-sized, psapery, petiolate, elliptic to elliptic-oblong leaves, short, short and shortly aristate stipules, terminal inflorescences with one or several fasciculate, subsessie to shortly pedunculate, subcapitate flower group enclosed by foliaceous bracts, short dentate calyx limbs, white salverform tubular corollas with slender tubes ca. 20 mm long and lobes ca. 10 mm long, and oblate fruits ca. 4 x 8 mm. The leaves have a widely looping submarginal vein. The flower heads are enclosed by ovate, perhaps whitened bracts 10-15 mm long that are generally persistent with the fruits. The fruits are laterally somewhat flattened.
Two varieties of this species were recognized by Steyermark (1967: 378), the typical variety, diagnosed by "peduncles absent", and var. pedunculata Bremek., with "peduncles present, 1-2.5 cm long", and noted these were sympatric which was unusual. Peduncle length varies widely and continuously in a number of Faramea species and this seems to be the case in Faramea sessiliflora. The illustration in the protologue shows the flowers head borne on very short peduncles, not sessile, and several collections now document peduncles of intermediate length (e.g., Pirani 1311). This variety thus no longer seems distinct and is not separated here.
Later Delprete (2006) reviewed this species and concluded that its two varieties are better treated as two species. He noted a difference in peduncle length between them, but separated them mainly based on other features. He distinguished these by peduncles 1-3.5 mm long, green bracts 12-15 x 5-7 mm, a truncate to undulate calyx limb, corollas with tubes 12-14 mm long and lobes 5-8.5 mm long, anthers 4.5-5 mm long, styles 10-11 mm long, and bracteate oblate fruits 3.5-5 x 8.4-11 mm in Faramea sessiliflora, vs. peduncles 5-25 mm long, pale orange bracts 20-28 x 7-17 mm, a calyx limb with developed linear lobes, corollas with tubes 20-25 mm long and lobes 9.5-10.5 mm long, anthers 2.8-3 mm long, styles 15-16.5 mm long, and ebracteate fruits 13-17 x 11-13 mm. The fruits he described for Faramea sessiliflora are remarkably large and rounded for the plants that agree with Bremekamps' type, and at least some of the fruiting specimens he studied are here treated as Faramea corymbosa (Lindeman 257, Mori & Bolten 8558), which has fruits of this size, and another was identified by Kirkbride as Faramea occidentalis (Feuillet et al. 10181), which also has large white corollas and large fruits. Delprete's separation of these species based on style and anther size and his detailed morphological description assume and indicate, respectively, that the flowers of both species are monomorphic so the anther and style lengths are species-level differences. This distinction does not work, though, or at least needs further study because specimens studied here that agree with his Faramea pedunculata are distylous (Pirani 1311, short-styled; Hatschbach 37589, long-styled with anthers ca. 5 mm long, the size given for Faramea sessiliflora). The development of the linear calyx lobes noted by Delprete is variable on the material seen, and no calyx lobs have been seen that are as long as those he described. The corolla sizes he described are distinct, but the material studied here has additional variation that blurs this distinction (e.g., corolla tube 16 mm long, intermediate between his species, and lobes 8 mm long, Thomas et al. 4505; corolla tube 22 mm long nad lobes 12 mm long, larger than he measured, Pirani 1311). A number of white-flowered species of Faramea vary by 100% or sometimes more in corolla size (e.g., Faramea occidentalis), so this character alone does not seem to separate two species.
Faramea sessiliflora is similar to Faramea corymbosa, which has developed peduncles bearing groups of smaller flowers enclosed by deciduous bracts. Faramea sessilflora is also similar to Faramea guianensis, with axillary inflorescences enclosed by larger bracts and smaller flowers. Faramea sessilflora is also often confused with Faramea sessilifolia, which differs markedly in its larger subsessile leaves and branched lax inflorescences with reduced bracts, and is usually confused only because of the similarity in the species names.