Graduation Date

Fall 2021

Document Type



Master of Science degree with a major in Biology

Committee Chair Name

Alexandru M. F. Tomescu

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Allison Bronson

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Christopher Berry

Third Committee Member Affiliation

Community Member or Outside Professional

Fourth Committee Member Name

Gar Rothwell

Fourth Committee Member Affiliation

Community Member or Outside Professional

Subject Categories



Important constituents of Siluro-Devonian floras, zosterophylls gave rise to the lycophytes. I explore the relationships of 18 zosterophyll species from 16 genera, maximizing sampling of anatomy. Using phylogenetic and phenetic methods, I (1) assess the influence of tree rooting, taxon sampling, and morphological vs anatomical characters on the stability of relationships; and (2) compare phylogenetic and phenetic methods in terms of relationships recovered. Phenetic analyses show sensitivity to taxon sampling and support placement of Renalia among zosterophylls, but do not provide results that are strongly congruent with those of phylogenetic analyses. Phylogenetic analyses demonstrate that taxon and character sampling significantly influence patterns of relationships. I consistently recovered two major clades: one, which lacks internal resolution and comprises the bulk of the zosterophyll taxa included in the analyses; the other clade includes the zosterophyll Ventarura and the lycopsid Sengelia, often accompanied by Discalis and Trichopherophyton (depending on taxon and character sampling). The placement of Sengelia in phylogenetic analyses supports earlier ideas that the zosterophyll ancestor of lycopsids had nonterminate fertile axes. Morphology- and anatomy-only analyses recover trees that differ from those obtained using morphology+anatomy, highlighting the importance of broader sampling of the morphological character space. Breadth of character sampling and not the amount of phylogenetic resolution should be the primary criterion for selecting between alternative hypotheses of relationships.

Citation Style

International Journal of Plant Sciences

Included in

Evolution Commons