This twice-compound leaf of the African wattle shows seven pairs of pinnae. The usual range is four to nine. Each pinna may have from 8 to 23 pinnules, those tiny olive-green, oblong leaflets with rounded tips produced on the tree in such vast numbers.

Keep counting and you are bound to find a pinna specimen with a pinnule count beyond the given range. In the world of living things the exceptions prove the rules. And people keep studying themselves and all around them because the last word on any subject will only be spoken once the last human is gone (Coates Palgrave, 2002; Schmidt, et al, 2002).