Hibiscus arnottianus subsp. arnottianus is a shrub or small tree that can grow up to 8 (occasionally 10) meters tall. The mature stems are glabrous, while the young stems, petioles, and calyces are glabrate. The leaves are simple and alternate, with ovate-elliptic to broadly ovate blades that are usually 4–10 cm long and 2–11 (up to 25) cm wide. The leaf apex is acute to sub-acuminate, and the base is obtuse to subcordate or cuneate. The upper surfaces of the leaves are glabrous or glabrate, while the lower surfaces are glabrate, with the blades being coriaceous. The margins can be entire or dentate throughout or near the apex. The petioles are usually less than half the length of the blades and can be copiously yellowish stellate pubescent. The stipules are subulate to filiform, 5–10 mm long, and caducous. The flowers are solitary and borne near the ends of the branches, with stout pedicels 1.5–6 (up to 9) cm long, which are articulate and glabrate. The involucral bracts are 5–7 in number, reflexed, linear-lanceolate to narrowly oblong, 5–8 (up to 10) mm long, and 1–2 mm wide, distinct or connate basally or adnate to the calyx at the base. The flowers are bisexual (perfect). The calyx is tubular, 1.5–2.8 cm long, with deltate-acute lobes 3–10 mm long, and is glabrate. The corolla is actinomorphic (radially symmetric) to moderately zygomorphic (bilaterally symmetric), with five white flaring petals, occasionally with a pink tinge on the abaxial side, and sometimes aging pinkish. The petals are 5–8 (up to 10) cm long from the point of insertion and are distinct from each other but adnate basally to the staminal column into a tube 1–3 (up to 4) cm long, convolute in bud, with the lower surface usually densely pubescent. The stamens are monadelphous, forming a staminal column that is exserted, pinkish to dark red (rarely white), and 8–19 cm long. The filaments arise in the upper third to half of the staminal column, are red or white, spreading, and are 0.8–3 cm long, with monothecal anthers. The ovary is superior, 5-celled or rarely appearing 10-celled by a vertical partition, with the carpels borne in a single whorl or rarely seemingly superposed whorls. The placentation is axile, with three or more ovules per cell. The style exceeds the staminal column and is 5-branched, with each branch terminated by an expanded stigma. The fruit is a loculicidal-dehiscent capsule that is chartaceous, obovoid-apiculate, approximately 1.7–2.5 cm long, glabrous, with a smooth, shiny endocarp and a reticulate-veined exocarp. The seeds are angular-reniform or rounded-reniform, about 4-6 mm long, yellowish-brown tomentose, and can be with or without endosperm. It is found in mesic to wet forests at elevations ranging from 120-790 meters.