Hydrangea arguta is a shrub 2-5 m tall. The stems have conspicuous deltate (triangular) to sub-rhombic leaf scars, hirsute, becoming glabrate. The leaves are opposite or in whorls of 3 per node, coriaceous (leathery), oblong-elliptic (long and round-oval shaped), elliptic, or oblong-oblanceolate (inversely lance-shaped) at 10-32 cm long, 3-9.5 cm wide, those of vegetative shoots often larger and broader, upper surface with conspicuously impressed veins, sparsely hirsute, glabrate with age. The lower surface has slightly raised veins, sparsely to densely hirsute, primarily along veins. The margins are crenate-serrate (scalloped-saw toothed), each tooth with a blunt forward appressed lobe or mucro, outer margin of each tooth revolute, apex acute to obtuse or acuminate, base cuneate to attenuate, petioles 0.3-8 cm long, dilated at base. The flowers are in corymbose panicles, usually 5-7 cm long and 8-12 cm wide, with the branches subtended by foliaceous sessile bracts 12-25 mm long and caducous. The staminate flowers 5-6-merous with lanceolate sepals, the lobes 1-5 mm long, petals greenish blue, pink to greenish white, yellow, or cream-colored, ovate (egg-shaped) at 3.5-8 mm long, staminal filaments unequal, 1-11 mm long, anthers purple to brown, pistillode nearly superior, 2-5 mm long, with ovules and a well-developed style and stigma, but these nonfunctional. The pistillate flowers are 5-6-merous with connate sepals more than 1/2 their length and adnate to ovary, the lobes lanceolate to ovate at 1-4 mm long, petals greenish blue to pink, triangular, 0.5-3 mm long, stamens absent, ovary urceolate, 5.5-6 mm long, style 0.5-3 mm long. The fruit is red to maroon, broadly ellipsoid to subglobose, 8-12 mm long, the flesh whitish. It produces many seeds that are elliptical and minute with fleshy endosperm. It is found in wet forests and occasionally in mesic forests between 300-2,000 meters.