Epiphytic or epilithic herb, erect or ascending from prostrate, rooting base. Stem loosely villous, 10 cm long when fruiting, green or reddish brown. Leaves in whorls of 1-4, basely attached; petiole 0.2-0.6 cm long, loosely villous; blade fleshy coriaceous, sometimes pink below, obovate or somewhat elliptic, 1-3.5 x 0.6-2.3 cm, margin not ciliate, apex rounded to emarginate, base acute, glabrous or loosely villous on upper surface, glabrescent, glabrous below; veins 3, obvious. Inflorescence solitary, terminal, erect; peduncle 1-2 cm long, villous, green or reddish brown; spike 2-7 cm long, green, densely flowered, rachis hardly ridged; floral bracts rounded, with scariose margin, glabrous, glandular. Fruits not sunken, subbasely attached, globose, green, apex with short, thick style and apical stigma.
Peperomia maguirei has some resemblance to P. quadrangularis but differs in having mostly obovate leaves that are slightly emarginate (with hairs in the indentation) vs. usually broadly elliptic leaves with continuous apex. The leaves in P. maguirei are in whorls of 1-4, whereas in P. quadrangularis they are strictly opposite. The fruits of the latter are sunken in the rachis, which is distinctly ridged (at least when dried), whereas the fruits of P. maguirei are not sunken and the rachis is not obviously ridged.