Metrosideros robusta, the northern rātā, is a forest tree endemic to New Zealand. It grows up to 25 metres or taller, and usually begins its life as a hemiepiphyte high in the branches of a mature forest tree; over centuries the young tree sends descending and girdling roots down and around the trunk of its host, eventually forming a massive, frequently hollow pseudotrunk composed of fused roots. In disturbed ground, or where there are gaps in the forest cover, Northern rātā will grow on the ground with a normal but short trunk.
Northern rātā is a massive tree, easily distinguished from other Metrosideros species by its small, leathery, dark green leaves which are 25-50mm long by 15-25mm wide, and have a distinct notch at the tip. Young growth is generally pink and covered in fine rust-coloured hairs that are gradually shed as the foliage ages but tends to persist at the midrib and in the vicinity of the leaf base. The flowers, borne in sprays on the tips of branches, are a mass of dark scarlet stamens. Flowering peaks between November and January, and seeds take a year or slightly more to ripen.
The greatest threat to Northern rata is browsing by possums which cause severe damage by eating the leaves, buds, flowers and young shoots of the tree. In severe cases this can lead to the death of the tree within two years.