Metrosideros waialealae var. waialealae is a shrub or small tree with fissured, flaky bark and narrow, pointed vegetative buds with spatulate scales 17 mm long and 9 mm wide. The leaves are simple and arranged oppositely. The blades range from ovate to lanceolate and occasionally broadly ovate, measuring 4–6 cm in length and 2–3(–4) cm in width, featuring an acute apex that can sometimes be drawn out and twisted. The bases are cuneate to rounded. The leaf surfaces are glabrous, with the margins being entire. The midrib is often red, adding a distinctive color contrast. The petioles are 10–20(–30) mm long and 2–3 mm wide, usually positioned at right angles or more to the stems, and are frequently red. Stipules are either vestigial or absent. The flowers are arranged in inflorescences of 4–6 pairs of cymules. These inflorescences are either glabrous or have appressed short pubescence. Peduncles measure about 13 mm long and 1.5 mm wide, while the pedicels are approximately 4 mm long and 1 mm wide. The bracts are either ovate or lanceolate, about 4 mm long and 3 mm wide, and are caducous. The flowers are bisexual (perfect) and actinomorphic (radially symmetric). The hypanthium, which is well-developed above the ovary, measures 3–4 mm in height and 3.5–5 mm in width, with the fruiting hypanthium extending 4–6 mm long and 5–8 mm wide, and often exhibits prominent veins that are glabrous or glabrate. The sepals are distinct and triangular, 1.5–2 mm long and 2–2.5 mm wide. The petals are obovate, 3–5 mm long and 2–3 mm wide. The numerous stamens stretch 1.5–2 cm long. The ovary is nearly superior, with numerous anatropous ovules and axile, peltate placentation. The style extends 2–3 cm long and ends with a small stigma. The fruit is a capsule enclosed by the hypanthium and prominently exserted. It is found on ridges between 600-1,300 meters.