Metrosideros polymorpha var. polymorpha is a tree ranging from 5-10 meters tall. This variety typically features robust, terete branches with rough and fissured bark, often peeling away in thick flakes, though it can also appear smooth and peel in long, thin strips. The vegetative buds are obovoid in shape. The leaves are simple and opposite, with orbicular to suborbicular blades measuring 1.5-6 cm in length and width. The apex is often retuse while the base is cordate. The upper surfaces may appear dull, glabrous, or somewhat shiny (notably in specimens from Oahu), while the lower surfaces are densely covered in gray or white wool. The coriaceous leaves display several pairs of raised veins radiating from the base, with an intramarginal nerve positioned 1-2 mm from the leaf margin. The petioles are pubescent, ranging from 2-4 mm long, and the stipules are either vestigial or absent. The flowers occur in inflorescences of 2–5 pairs of cymules, with all parts densely white-woolly, including the calyx and calyx lobes, and partly the petals. The bracteoles are ovate, rounded, and woolly, measuring 3-5 mm. The hypanthium is 3–7 mm high and 3–8 mm wide. Flowers are red, pink, or orange, bisexual (perfect), and actinomorphic (radially symmetric), with very short pedicels of 1-3 mm. The sepals, including rounded lobes, are white-woolly, large, and broad at 5 mm. The petals are also white-woolly and rounded. Stamens measures approximately 2 cm, with a nearly superior ovary and a protruding style about 23 mm long. The fruit is a densely woolly capsule, about 6-7 mm long, and is exserted from the calycine tube. It is found in shrublands and mesic to wet forests between 30-2500 meters.