The Bottlebrush tree is a small flowering tree that derives its common name from the shape of its bright red flowers which as you can see in the image above look a lot like a bottle brush. This tree has a close cousin called the "Weeping Bottlebrush tree" (Callistemon viminalis) that is somewhat more popular as an ornamental tree than this one. The difference being mainly that the "weeping" variety has branches that droop down while this one´s are more rigid.
The flowers grow on the ends of the branches and after they fade a series of "knobs" are left in their place that stay of the tree for a year or more. These knobs also create an interesting ornamental effect.
From my observation the C. rigidus has fewer flowers than the c. viminalis although the flowers themselves are very similar. In both cases the flowers grow along the length of the new stem.