Graduation Date

Fall 2023

Document Type

Thesis

Program

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

Terry Henkel

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Michael Mesler

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Gar Rothwell

Fourth Committee Member Affiliation

Community Member or Outside Professional

Subject Categories

Botany

Abstract

Cladoxylopsids are seed-free plants that formed the world’s earliest forests and gave rise to horsetails (sphenopsids), but their evolutionary origins are poorly understood. Here, I describe a new Early Devonian cladoxylopsid from the Emsian (400-395 Ma) Battery Point Formation (Québec, Canada). The structural features of this plant indicate taxonomic affinity to cladoxylalean cladoxylopsids and its phylogenetic position supports placement in genus Cladoxylon (the proposed name, Cladoxylon kespekianum sp. nov., to be formalized by peer-reviewed publication). Specimens of this plant are permineralized in calcium carbonate and were studied using the acetate peel technique with light and electron microscopy. Cladoxylon kespekianum is a large plant with stele consisting of 9-13 long primary xylem ribs, some of which coalesce toward the axis center, and with lateral appendages supplied by terete xylem strands and arranged helically or in irregular whorls. This plant joins Psilophyton and Kenrickia as the best characterized anatomically and largest Early Devonian euphyllophytes. Cladoxylon kespekianum is one of the oldest representatives of the cladoxylopsid group and pushes the age of complex vascular architecture deeper in time. However, data on branching anatomy and architecture, reproductive structures, and roots are needed for this new plant to be understood as a whole organism.

Citation Style

Amer. J. Botany

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