Characters anatomical

Another way of obtaining indirect information on molecular evolution was offered by the study of phylogenetic trees. A typical example, in this field, is the comparison between amphibians and mammals. Both groups derived from a common aquatic ancestor, but amphibians evolved much more slowly. They share so many anatomical characters that a single order comprises most of them, while mammals differentiated into as many as sixteen distinct orders. Mammals clearly underwent a much faster phenotypic evolution than amphibians, and it seemed logical to conclude that, at the molecular level, the mutation rate has been much faster in mammals than in amphibians. 

We also discuss the relative advantages of using molecular versus anatomic characters in phylogenetic analyses, and point out that molecular data can provide more characters and use better phylogenetic methods, but anatomic characters, which are individually more informative, can be obtained from fossils as well as living organisms and allow easier characterization of homoplasy. 

Anatomical characters of thallus structure play a large role in the delimitation of foliose and fruticose genera. The constancy of axil formation of different types Usnea, Alectoria, Letharia, and Anzia), veins (Peltigera, Hydrothyria), supporting tissues (Ramalina), and ground structure of cortical formations (hyphae anticlinal versus periclinal, in Physco-nia versus Anaptychia, Physcia versus Heterodermia etc.) have frequently been confirmed. They are valid systematic criteria and will not be discussed further here. 

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