Geniostoma helleri is a shrub that can grow 2–4.5 meters tall and may sometimes climb. The stems are cylindrical, somewhat divaricately branched, and glabrous. Its leaves are simple and opposite, oblanceolate to elliptic or occasionally elliptic-ovate blades measuring 5–14 cm long and 1.7–4 cm wide. The apex ranges from acute to short-acuminate, and the base from broad to narrowly cuneate. The leaf surfaces are glabrous and membranous, with flat margins and veins that are scarcely impressed and inconspicuous. The petioles are glabrous, 0.7–1.5 cm long, and the stipules are connate into a cup 1–5 mm long, closely appressed to the stem, glabrous, and persistent. It produces flowers in terminal inflorescences with 3–9 or more flowers in pendulous or erect, compound, paniculate cymes. These are glabrous, with peduncles 5–20 mm long and pedicels 6–9(–15) mm long, extending to 10–30 mm in fruit. The flowers can be bisexual (perfect) or functionally unisexual, with a 5-merous calyx whose sepals are united at the base. The corolla is 5-merous, campanulate to rotate, either white or pale greenish-yellow, and 9–11 mm long. Stamens are alternipetalous, attached to the mouth of the corolla, and exserted. The ovary is superior or partly inferior, with 2 or 3 locules and numerous amphitropous ovules. The fruit is a lanceoloid to ovoid capsule, 9–20 mm long, 2(3)-valved, with longitudinally striate valves, and matures from whitish green to green, sometimes with a black-purple tinge, usually turning brown-black when over-mature. The seeds are numerous, ellipsoid to subglobular, and embedded in juicy orange to red pulp. They have a thick, fleshy, and oily endosperm, and the seed surface is minutely papillose. It is found in diverse mesic forests and valleys between 240–1,190 meters.