Peperomia mauiensis is a fleshy herb with brownish purple stems, ascending to erect from a short repent base, measuring 10–20 cm long and 2–3 mm in diameter toward the base. The stems are usually branched, with internodes 2–5 cm long, densely strigillose on the upper parts, and older stems becoming glabrate. The leaves are simple and whorled, with 3–5 (sometimes up to 9) per node. The blades are oblong–spatulate to obovate, measuring 1.2–2 cm long and 0.4–1 cm wide. The apex is rounded, and the base is narrowly cuneate. The surfaces are hirtellous or sometimes glabrate on the upper surfaces; they are dark green or reddish green with pale green veins, producing a mottled appearance. The leaves are thin and fleshy, drying to a chartaceous texture. The margins are entire, with only the midrib being conspicuous, or the leaves are inconspicuously palmately 3-veined. The petioles are 0.3–0.5 cm long, somewhat appressed-hirtellous to glabrate. Stipules are absent. The flowers are in solitary and terminal spikes, measuring 4–6 cm long, with the rachis about 0.5–1 mm in diameter, glabrous. The flowers are moderately to loosely congested, with slender peduncles 3–5 cm long, but at least some of them more than 3 cm long, strigillose to glabrate. The flowers are bisexual (perfect), with the perianth absent. A peltate bract subtends each flower. The calyx (sepals) and corolla (petals) are absent. There are two stamens. The ovary is superior, broadly ovoid, 1-carpellate, 1-celled, with an oblique apex and 1–4 subterminal stigmas. The fruit is broadly ovoid, about 0.8 mm long, and viscid with sessile glands. There is one seed per fruit, with scanty endosperm and copious starchy perisperm. It is found in mesic valleys between 40-600 meters.