Paleobotany, Taxonomic Classification, and Phylogenetics

Abstract

The preceding chapters reviewed our knowledge of genetic diversity in conifers from the genome to populations and species, from SNPs to phenotypic variation in morphological and adaptive traits controlled by dozens or even hundreds of genes. In this chapter we look at the diversity of conifers at the species, genus, and family levels, and the evolutionary relationships among them. As the title of this chapter implies, the scope of discussion is large which will almost assuredly result in the superficial treatment of some areas that have garnered considerable scientific enquiry. Our objective, nevertheless, is to capture current views on the number of extant conifer species, how they are classified, from whence they came, and how they are related to one another. In doing so, we hope to avoid confusion associated with the numerous and often nuanced definitions of terms such as taxonomy, systematics, classification, and phylogenetics (Mayden 1992; Stevens 1994; Singh 2004; Wiley and Lieberman 2011). In the treatment presented here we define taxonomy simply as the discipline of discovery, description, naming, and classification of groups or taxa, typically species, genera, and families. Taxonomy today is based upon, and richly informed by, phylogenetics, the study of the evolutionary relationships between taxa. Current hypotheses of phylogenetic relationships among and within conifer families, and thoughts on the origins of conifers are summarized here, along with estimates of times of divergence for major taxa based on fossil records and molecular clock studies.