Surviving ancestors, hard polytomies, and seed plant evolution

Forty years of phylogenetic analysis have failed to resolve the relationships among the major groups of seed plants. From the fossil record it is clear that more seed plant groups have gone extinct than are extant, though some direct ancestors of today's clades could have survived. Here we reanalyze morphological matrices relevant to seed plants, applying two underutilized visualization tools: Networks for displaying incompatible phylogenetic signal and Romerograms (spindle diagrams) for depicting alternative relationships, suspected budding speciation, and surviving ancestors. Surviving ancestors give rise to hard polytomies, and networks may help pinpoint them as suggested by experiments in which we added simulated ancestors to our matrix. Romerograms - whose reproducible construction we illustrate - offer a heuristic means of representing phylogenetic hypotheses, and we argue that the field's near-exclusive focus on identifying sister groups and representing them in cladograms may have driven phylogenetics into an impasse. Identifying true evolutionary polytomies warrants further methodological research, but broadening the repertoire of data visualization approaches may help overcome the field's entrenched bias toward strictly dichotomous trees.