Classification has always been about putting similar things in the same box. It is how one defines “similar” that changes. The earliest classifications were presumably pragmatic: things you could eat in one box, things you couldn’t eat in another, things you could use for medicines in yet another. In modern classification the idea of evolution determines what is thought to be similar. Hence, one criterion is that all the organisms in the one box should have evolved from a recent common ancestor. No problem there: both Banksias and Dryandras can be assumed to have a recent common ancestor. It is the second criterion that is tricky: all the descendants of a recent common ancestor should be in the same box. Dryandras can be assumed to have evolved from within the Banksias and therefore this criterion requires that they both be in the same genus.
Let us see what happens if we apply these criteria to humans. The mnemonic for remembering the higher classifications is: King Philip Came Over For Good Soup. (Kingdom, Phylum, Class, Order, Family, Genus, Species.) We are in the Kingdom Animalia, Phylum Chordata, Sub-Phylum Vertebrata, and Class Mammalia. Other Classes at the same level are: jawless fish (lampreys and the like); cartilaginous fish (sharks and rays); bony fish; amphibians; reptiles; and birds. Reptiles includes lizards and snakes, crocodiles, turtles and dinosaurs.
The first problem is that birds certainly evolved from dinosaurs. The reptile class therefore does not include all the descendants from the one ancestor; birds must go into the dinosaur box. The next problem is that mammals must have evolved from primitive reptiles, so by the same logic, mammals must also go into reptiles. Those of you who think that Dryandras should be sunk into Banksias must therefore think of themselves as hairy lizards.
But wait, there is more. Where did reptiles evolve from? Surely from bony fish. So reptiles and fish should not be at the same level: reptiles, together with birds and mammals, all must go into the fish class. You are not hairy lizards after all: you are hairy, air-breathing fish.
Or we could decide that it was rather silly and abandon the second criterion.
Jim Barrow