Skewed Distribution of Species Number in Grass Genera: Is It a Taxonomic Artefact?
A striking pattern for distribution of taxa in their respective higher categories points to a skewed distribution towards monotypic and small groups. This phenomenon was first documented by Willis
and Willis and Yule
in a study of the flora of Ceylon (Sri Lanka). They dubbed this pattern the
hollow curve distribution (HCD) and indicated that such a pattern exists at all taxonomic levels. Willis and Yule
asserted that the longer the group has existed, the more area it will occupy. They further stated that monotypic genera are in general ‘beginners’ and are descendents of larger ones. The HCD was later demonstrated in other organisms, such as arthropods, birds and mammals