Coprosma ernodeoides is identified as a many-branched, prostrate, and trailing shrub, often found spreading across the ground and sometimes rooting at the nodes. The stems are typically 2–3 meters long, featuring numerous short, ascending lateral branches that usually do not exceed 20 cm. Younger branches display an angled and hispidulous (minutely bristly) surface. The leaves are simple and arranged oppositely, closely spaced, and often appear fasciculate due to clusters forming on short lateral branches ranging from 1 to several centimeters long. The blades are linear–lanceolate, measuring 6–13 mm in length and 1.5–3(–4) mm in width. They are glabrous, glossy, coriaceous (leather-like), and stiff, with margins that can be either hispidulous or glabrous. The leaves may be petiolate or sessile, with stipules that are adnate to the leaves, forming a truncate, stipular cup approximately 1.5 mm high, which can be hispidulous and dentate with a few small appendages. The flowers are solitary, terminal, and 4-merous, with a sessile arrangement. The species is dioecious (having separate male and female plants), often heterostylous, and relies on insects for pollination. Male flowers lack a calyx, while female flowers have a 4-toothed calyx. The corolla may vary, being narrowly campanulate in male flowers and tubular in female flowers, with a nectary disk usually present. The ovary can be inferior to occasionally partly so or very rarely superior, containing 2(-4) cells with one ovule per cell. The style is divided nearly to the base, with long-exerted, papillose-hirsute stigmas. The fruit is a juicy, glossy black drupe, ovoid in shape and 8–13 mm long, containing 2(-4) one-seeded, planoconvex pyrenes. The seeds have a well-developed oily endosperm, although in some cases, the endosperm may be scant or absent. It primarily inhabits open sites, often found on lava and cinder fields within subalpine woodlands. However, it has also been collected in wet forests and potentially bogs between 1,220 – 2,590 meters.