Geniostoma degeneri is a shrub that grows between 1.5 and 3.5 meters tall. The stems are terete (cylindrical) to weakly angled and are either hispidulous or glabrate. The leaves are simple and opposite, with blades that are elliptic to broadly elliptic, sometimes elliptic–obovate or elliptic–ovate, measuring (3.5–)5–14.5 cm long and (1.5–)3–7.4 cm wide. The apex is abruptly short-acuminate to acuminate and sometimes slightly falcate. The base is sub-truncate to cuneate. The upper surfaces are glabrous, while the lower surfaces are sparsely hirtellous, sometimes with only a few scattered hairs or completely glabrous. The leaves are medium green on the upper surface and pale green underneath, with a thin and coriaceous texture. The margins are flat, entire, or rarely toothed. The upper surface has slightly impressed veins. The petioles are (0.5–)1–2 cm long. Stipules are interpetiolar and may also be intrapetiolar, membranous, and connate into a cup 6–11 mm long, quickly splitting and adnate to the lower few millimeters of the petioles. The flowers occur in terminal, dense, glabrous, sessile cymes, with each inflorescence containing 3–10(–15) flowers. Pedicels are 1–3 mm long, and the bracts are linear–filiform, measuring 6–7 mm long. Bracteoles are filiform, approximately 6 mm long. Flowers are bisexual (perfect) or functionally unisexual and actinomorphic (radially symmetric). The calyx is 5-merous, with sepals united at the base, lobes slightly unequal, and inner lobes narrower and more membranous, oblong–lanceolate to narrowly lanceolate, sometimes the outermost being ovate, 6–15 mm long, and 3–4 mm wide. The veins are obscure and glabrous, and margins are hyaline, imbricate in bud, with the inner surface often having colleters at the base and mostly fimbriate margins. The corolla is 5-merous, orangish-yellow, 18–19 mm long, white with a yellow or green tinge, and campanulate to rotate. The tube gradually narrows toward the mouth, is 10–11 mm long, glabrous externally, and sparsely white hirtellous within, with hairs present in the throat and mouth and often extending onto the lobes. The lobes are linear-lanceolate, 8–10 mm long, with an attenuate-acute apex, and are imbricate or contorted in bud. The five stamens are alternipetalous, attached to the mouth of the corolla, exserted, and usually recurved after anthesis. They are either glabrous or hairy, with mostly short filaments and anthers that are 2-celled, introrse, and have a connective that often extends to form an apical appendage, opening by longitudinal slits. The ovary is superior or partly inferior, with carpels that are either hairy or glabrous. It is 2– or 3-locular, sometimes with imperfect partitions in the upper part of the ovary. The ovules are numerous and amphitropous, with axile placentation. The style is terminal and mostly short, and the stigma is clavate, ellipsoid, or globular, sometimes ± oblong, about as large as the ovary. The fruit is a white and slightly fleshy capsule at maturity, narrowly ovoid–ellipsoid, or sometimes narrowly obovoid–ellipsoid. It is compressed, measuring 20–30 mm long, with two dorsally keeled valves. The keel is 1.5–2 mm wide, and the apex has a 1–2.5 mm long beak. The capsule dehisces septicidally to sub–septifragally and matures to green, sometimes with a black–purple tinge, eventually becoming brown–black when over-mature. The seeds are pale brown to black and 1.5–2 mm long. They are embedded in juicy orange to red pulp, numerous, ellipsoid to subglobular, and intruded on the hilar side. The surface is mostly minutely papillose to areolate. The endosperm is thick, fleshy, oily, and proteinaceous, with saccharose or hemicellulose. The embryo is small and straight. It is found in diverse mesic and wet forests between 1,090-1,220 meters.