This species has medium-sized elliptic leaves with a looping, weakly developed submarginal vein, well developed stipule aristas, lax terminal and sometimes axillary inflorescences with pedicellate showy flowers generally in cymes of 3, developed usually truncate calyx limbs, salverform white corollas with long-acuminate lobes, and subglobose to oblate fruits. Specimens of this species frequently dry dark gray to blackened. Their leaves are rather stiff-textured with quite waxy surfaces, so they often do not stick well to the glue of herbarium specimens. The venation is usually not much raised or prominent, and the secondary veins 5-12 pairs. The flowers are borne on well developed pedicels, and nocturnal and fragrant. The corollas are white to cream, and become yellowed when old. They vary widely in size, with tubes 12-22 mm long and lobes 8-25 mm long, but generally have the lobes about as long as or a bit longer than the tube. The flowers last one day (or night) and the corollas are not frequently collected at anthesis. Faramea occidentalis is widespread and often grows in secondary vegetation, and is commonly collected; it is the only Faramea species found in the Antilles.
This species is quite variable morphologically in features such as leaf size, number of flowers and laxness of the inflorescence, and flower and fruit size. Similar variation is found in most regions and seems to be correlated at least in large part with humidity and disturbance of the habitat. Steyermark named several varieties and subspecies of Faramea occidentalis, but these seem either to represented distinct species or not separable taxonomically. These varieties were discussed in some detail by Taylor et al. (2004: 595). Also as noted there Faramea stenopetala is very similar to Faramea occidentalis and their separation probably deserves further study.
In terms of variation within Faramea occidentalis, some notable forms are some of the plants from Veracruz, Mexico, which have quite short, few-flowered umbelliform inflorescences. Other plants from the Golfito region in southern Costa Rica have robust leaves and robust inflorescences with numerous flowers and elongated stout axes. Faramea belizensis was separated based on its leaves with the venation mostly well developed abaxially, 13--15 pairs of secondary veins that are united in a well developed submarginal vein, and terminal inflorescence with a single peduncle and the secondary axes 3--4-verticillate. These plants have been collected infrequently at 900-1100 m in Belize and Honduras. These plants were included by Borhidi (2012) within the circumscription of Faramea occidentalis, but appear to differs consistently in several morphological features and are separated here. Faramea standleyana is known from one specimen from lowland Guatemala that differs from Faramea occidentalis by its relatively short dentate calyx limb and somewhat small corollas; it may be only a small form of Faramea occidentalis, but is provisionally recognized here until further study clarifies its status. Faramea chiapensis is also similar to Faramea occidentalis, but not well known and found at relatively higher elevations; this is separated here provisionally at least until it is better known.
Faramea occidentalis is similar to Faramea orinocensis, with consistently smaller leaves that are rounded at the base, quite short petioles, and smaller inflorescences. Faramea occidentalis is also similar to Faramea neblinae of wet montane tepui vegetation, which lacks developed stipule aristas. Faramea occidentalis is also similar to Faramea teniflora, which has consistently rather small elliptic leaves, fewer-flowered inflorescences, corollas with the tubes significantly longer than the lobes, and generally smaller fruits. Faramea occidentalis is also similar to Faramea montevidensis. Faramea occidentalis is also generally similar to Faramea nigrescens of east-central Brazil, which is found in dryer vegetation and has smaller flowers and fruits.