The analytic orientation of this paper is intended as a replacement for the antiquated but still prevalent phylogenetic inferential models and techniques of the late 20th century that are focused entirely on shared descent. Serial descent, that is, progenitor to descendant, may occur at the species or infraspecies level. In molecular systematics, species level paraphyly occurs when two examples of the same species are separated on a cladogram by a second species. This implies linear macroevolution of the second species from the first. Molecular cladograms often show cladistic structure (branching) among examples of the same species. If well-supported, such indicates a potential for evolution. A range of infraspecific and intraspecific cladistic structure in species of Pottiaceae (Bryophyta) was demonstrated in previously published molecular cladograms and data sets of other authors. This includes well-supported cladistic structure of molecular strains, and well-supported paraphyly involving other species. Large numbers of base pair changes among strains are considered here evidence of evolvability and increasing age of a species. Infraspecific strains are apparently lost in older species through speciation and extinction. Cluster analysis using DNA metadata of Oxystegus species matched published molecular cladograms to a large extent. The fact that apparent molecular strains are present in both nonparaphyletic and paraphyletic species, about half the species studied, shore up the theory that internal racial differentiation at the molecular level leads to or signals serial descent of multiple extant morphotaxa. It is because much infraspecific molecular cladistic structure exists that newly speciated taxa are already strongly cladistically dichotomized. Thus, the ultimate source of molecular paraphyly is internal to each species, and does not imply polyphyly by convergent species or cryptic taxa. Molecular systematics cannot effectively model progenitor-descendant radiation. Species with many strains are potential sources of future biological diversity. Recognition of differential evolvability may allow facilitation of complex, interactive, diverse ecosystems successfully tracking climate change.
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