Some may be taxonomically unique the last representative of an otherwise extinct group of animals, like the duck-billed platypus or the long-beaked echidna while others may differ from each other only slightly.

ECONOMIST: Green.view: Finger on the spot | The

The 9-9-9 Plan is a member of what I call the family of taxonomically equivalent tax systems, which define the tax base in an economically proper manner, albeit in different forms, and minimize the deadweight-loss tax burden on the economy.

FORBES: Herman Cain's Tax Plan Is a Winner, But Here's Your Exploding Cigar