Pittosporum hosmeri is a shrub that grows 0.7–1.75 meters tall. Its young parts are densely covered with reddish brown to brown tomentose, which may occasionally be part pale brown and part whitish. The stems are gray to medium brown and exhibit a tomentose texture that becomes less pronounced as they mature (subglabrate). The leaves are simple and alternate with blades broadly to narrowly obovate or spatulate, measuring 3.5–7 cm long. The leaf apex can be obtuse to rounded or acute, sometimes even short-acuminate, with an attenuate base. The upper surfaces of the leaves feature prominently impressed veins and bear a ± pale brown to reddish brown tomentose, which becomes less dense with age, turning glabrate; the lower surfaces are densely covered in tan to golden yellow tomentose. The leaves are subcoriaceous to coriaceous, moderately rugose, with entire margins that are slightly to strongly revolute. They have 5–9 pairs of lateral veins and petioles that range from 0.5 to 5.5 cm in length. The flowers occur in dense tomentose inflorescences, with peduncles ranging from 3–25 mm long and slender pedicels measuring 2–32 mm. The flowers are functionally unisexual, forming in groups of 5–14 within terminal, axillary, or cauline simple corymbose inflorescences. The calyx is broadly cup-shaped with five distinct sepals lanceolate to broadly ovate or suborbicular, measuring 2–7 mm long. The corolla comprises five white to cream petals, each 13–23 mm long. It has five stamens that alternate with the petals. The fruits are ovoid to broadly ovoid capsules, approximately 20–35 mm long. They are initially densely covered in brown to reddish brown tomentose, which sparsely remains at maturity. The capsules have a rounded to obtuse apex, and their surface is deeply rugose-tuberculate or sulcate. Each capsule contains about 30–50 black to brown or reddish black seeds, irregularly angled and compressed, measuring 6–8 mm long. It is found in dry to wet forests and subalpine forests between 180-2,200 meters.