Nothofagus solandrivar.solandri, commonly called Black beech (Māori: tawhai rauriki), is a variety of the tree species Nothofagus solandri, endemic to New Zealand. Black beech occurs on both the North and the South Island at low altitudes up to the mountains. The other variety of N. solandri is called Mountain beech or Nothofagus solandri var. cliffortioides, and grows at higher altitudes than black beech.
Black Beech (var. solandri) is a medium-sized evergreentree growing to 27 m tall. Mountain Beech (var. cliffortioides) is smaller (20 m) and near the treeline forms a "goblin forest" where the trees are no more than 2 m tall.
The leaves are alternately arranged, ovoid, 10 mm long and 5 mm broad, with smooth margins. In var. cliffortioides the leaves are more elongated and have a pointed end, while var. solandri has shorter rounder leaves. There is however considerable variation in leaf shape within the varieties, and hybridisation occurs between the varieties.
Var. solandri is known as Black Beech because it is prone to a sooty mold which covers the trunk and branches. This in turn is the result of a scale insect which sucks sap from the tree, and excretes honeydew a sweet liquid in small droplets (less than 1 mm diameter) on the end of stalks. This feeds the sooty mold, and also forms a valuable high energy food source for various birds and insects including the Kākā. The infestation is common and does not appear to harm the tree.
Both varieties have been planted in Great Britain and var. cliffortioides has shown better cold tolerance than var. solandri in locations such as Scotland.