This species is characterized by its elliptic to obovate, petiolate leaves with a rounded to cordate base, pyramidal multiflowered inflorescences, 5-merous flowers, corollas with the tube 3.5-4 mm and the lobos 3-3.5 mm and acute. and woody, suglobose to ellipsoid capsules 1.5--2.5 cm in diameter. The specimens characteristically dry with a brownish red color. The corolla lobes are thinly imbricated or perhaps valvate, or almost so. The inflorescences are multiflowered but usually only one to five fruits are produced from them. The fruits of Simira salvadorensis vary a bit in size, though less than in some other Simira species and apparently to some extent in correlation with the number of fruits that develop.
The leaves vary rather markedly in size among plants, across the range, and on different branches of some individual plants (e.g., Aguilar M. 7405). In general the leaves show a size gradation with smaller leaves in the northern to central part of its range and larger leaves in the southern part, though much variation is evident in local areas. This species is apparently sometimes deciduous, and leaf size may be correlated with humidity of the environment. Simira salvadorensis also shows variation in leaf pubescence, from glabrous to puberulous or hirtellous below; this feature may be correlated in part with leaf age, with the pubsescence denser and generally distributed on leaves that are flushing and then apparently deciduous as the leaves mature. The leaves also show notable variation in form, especially of the blade base, but are consistently widest above the middle. The extreme variants of these features are often distinctive, but they are linked by intermediate forms and uncorrelated with each other. Simira salvadorensis is circumscribed here to include this variation, following Lorence et al. (2012). Borhidi (2012) took another view, and separated these plants into four species based mainly on leaf size, shape, and pubescence. These do not differ in reproductive characters (the small fruits of his Simira lancifolia fall within the range now documented for plants that fall into his Simira salvadorensis) and some of the critical leaf features are generalizations rather than complete distinctions, so those species are synonymized here pending documentation of clearer morphological and geographic distinctions.