Geniostoma tinifolium var. wahiawaense is a shrub or small tree reaching heights of (1.2–)2–8(–15) meters. The stems are dichotomously branched, young branches are terete (cylindrical) or nearly so, and glabrous. The leaves are simple, opposite, with blades that are elliptic to elliptic-oblanceolate, sometimes narrowly elliptic, oblong-elliptic, or lanceolate, measuring (3.8–)4.5–21 cm long and (1.4–)2–5(–7.3) cm wide. The leaf apex is abruptly acuminate to acute, and the base is narrow to sometimes broadly cuneate, ± asymmetrical. The surfaces are glabrous, medium green, and membranous, with flat margins. The veins are not impressed on the upper surface. The petioles are 0.6–2.2(–4) cm long, and the stipules are interpetiolar, sometimes intrapetiolar, completely connate, forming a truncate sheath 1–4 mm long, occasionally splitting with age, slightly adnate to the base of the petioles, and the margins are sometimes ciliolate. The flowers are in terminal inflorescences, with (3–)9–12(–19) flowers in pendulous, open, paniculate cymes. They have a semen-like fragrance and are glabrous throughout. The peduncles are weakly recurved, 9–22 mm long, elongating to 13–25(–35) mm long in fruit. The pedicels are 8–11 mm long, elongating up to 23 mm long in fruit, and the bracts and bracteoles are subulate, 0.7–1.6 mm long. The flowers are bisexual (perfect) or functionally unisexual, actinomorphic (radially symmetric). The calyx is 5-merous, with lobes connate slightly to about ½ their length, imbricate, ovate-deltate, 1.5–3 mm long, and 0.7–1.6 mm wide. The inner surface of the calyx often has colleters at the base, and the margins are hyaline and ± ciliolate. The corolla is 5-merous, pale or greenish-yellow, narrowly urceolate, 17–19 mm long, with a 5.5–7.8 mm long, sparsely white pilose tube. The lobes are imbricate or contorted in bud, ovate-deltate or ovate, 1.7–2.3 mm long, with a short-acuminate to rounded apex. The stamens are 5, alternipetalous, attached to the mouth of the corolla, exserted, usually recurved after anthesis, glabrous or hairy, with primarily short filaments. The anthers are 2-celled, introrse, with the connective often extended to form an apical appendage, opening by longitudinal slits. The ovary is superior or partly inferior, glabrate, 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, with a clavate stigma, ellipsoid to globular, sometimes ± oblong, about as large as the ovary. The fruit is a capsule that is broadly ovoid to subglobose-ovoid or ellipsoid-ovoid, measuring 8–17 mm long, 2(3)-valved, septicidal to sub-septifragal, with valves that are transversely wrinkled and not keeled. The apex has a beak 0.5–1.5 mm long, maturing to green, with or without a black-purple tinge, and usually becoming brown-black when over-mature. The seeds are ± winged at both ends or all around, embedded in juicy orange to red pulp, numerous, ellipsoid to subglobular, intruded on the hilar side, with a surface that is mostly minutely papillose to areolate, brown, about 3 mm long. The endosperm is thick, fleshy, oily, and proteinaceous, with saccharose or hemicellulose, and the embryo is small and straight. It is found in wet forests between 300-920 meters.