Graduation Date

Spring 2024

Document Type



Master of Science degree with a major in Biology

Committee Chair Name

Alexandru Tomescu

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Gar Rothwell

Second Committee Member Affiliation

Community Member or Outside Professional

Third Committee Member Name

Kelly Matsunaga

Third Committee Member Affiliation

Community Member or Outside Professional

Fourth Committee Member Name

Oscar Vargas

Fourth Committee Member Affiliation

HSU Faculty or Staff


Secondary xylem, Wood anatomy, Fossil, Devonian, Euphyllophyte, Tracheid, Gymnosperm, Taxonomy, Metric, Quantitative comparison

Subject Categories



The oldest woody growth has been recognized in several Early Devonian (ca. 410-395 Ma) euphyllophytes. Their taxonomic diversity is difficult to evaluate due to a lack of quantitative methods for comparing plants based on secondary xylem anatomy. In turn, this hinders understanding of their implications for the evolution of plant development. To develop metrics that quantify secondary xylem anatomy and allow for conclusive comparisons, I investigated extant taxa and Early Devonian fossil woody taxa. I developed multiple metrics for quantifying tracheid size as a function of position in the secondary xylem and tested them on a dataset of extant gymnosperms. The four metrics that showed consistent trends within taxa and captured differences among taxa were applied to both previously recognized and previously undescribed Early Devonian woody taxa to evaluate taxonomic diversity and placement of the new fossils. The four new secondary xylem metrics, considered alongside other anatomical characters, allowed assignment of two of the new fossils to the previously described species Frahueberia gerriennei and enabled the recognition of two putative new woody euphyllophyte taxa. The secondary xylem metrics I developed are effective in demonstrating conspecificity and in separating distinct woody taxa, especially in combination with data on the primary xylem and xylem rays. They provide a new method for assessing the taxonomic placement of fossils with incomplete preservation, opening up new avenues for exploring fossil plant diversity and for characterizing anatomy with implications for the evolution of plant development.

Citation Style




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