Xanthorrhoea johnsonii are Grass Trees that have a trunk that is typically black as a result of bush fires, hence the nickname “Blackboy”.
They are typically single trunked specimens that grow up to 5 metres tall. Minor changes in their trunk direction are usually caused by new growth after the tree flowers. Major bends or multiple heads in the the trunk of a grass tree can be caused by accidents – eg another tree falling on to the apex or pushing the grass tree over. Usually it will attempt to continue growing vertically. Every tree is unique and has years of history reflected in its shape.
In poor bush soil the trunk of a grass tree will grow approx 9mm per year. A tree with a metre high trunk could be 100 years old. In better soils, growth can be faster and trees are more likely to grow multiple heads.