Geniostoma cyrtandrae is a shrub growing between 0.7 to 1.5 meters tall, sometimes reaching up to 2 meters. The stems are fleshy, cylindrical to weakly angled, flattened when dry, covered in short, hispidulous hairs. New branches emerge from the uppermost axils below the inflorescence. The leaves are simple and opposite, clustering at the ends of branches, with obovate to broadly elliptic or occasionally oblanceolate blades measuring 15 to 30 cm in length and 4 to 14 cm in width. The apex is abruptly acuminate to somewhat cuspidate, and the base ranges from broad to narrowly cuneate. The upper leaf surfaces are glabrous, while the lower surfaces are moderately or sparsely short-hispidulous with strongly curved hairs. The leaves are dark green on the upper surface and pale green on the lower, with a thick texture and flat, entire, or rarely toothed margins. Petioles are 1 to 5 cm long. Stipules are interpetiolar or intrapetiolar, membranous, forming a cup-like structure 3 to 7 mm long, and are deciduous. The flowers are in terminal, compound paniculate cymes, numbering from 8 to over 80, with a densely puberulent texture consisting of appressed to spreading hairs. The peduncles are erect, measuring 0 to 10 mm long, with reflexed branches 10 to 40 mm long and pedicels 5 to 17 mm long. The flowers, which can be bisexual or functionally unisexual, have a 5-merous calyx with sepals united at the base and pale green, slightly unequal lobes. The corolla is greenish-yellow or pale yellow, 20 to 35 mm long, with a narrowly urceolate tube and linear-lanceolate lobes. The stamens are exserted and attached to the mouth of the corolla. The superior or partly inferior ovary has 2 or 3 locules, densely pubescent in the upper half. The fruit is a lanceoloid-ellipsoid capsule, 32 to 35 mm long, with two valves and a 5 to 7 mm long beak. The seeds are numerous, ellipsoid to subglobular, pale brown to black, about 2.5 to 3 mm long, embedded in juicy orange to red pulp, and typically winged at both ends. They contain a thick, fleshy, and oily endosperm, and the seed surface is mostly minutely papillose to areolate. It is found primarily in the mesic valleys and forests of the Ko’olau Mountains and the Wai’anae Mountains of O’ahu between 300-520 meters.