Graduation Date

Spring 2024

Document Type



Master of Science degree with a major in Biology

Committee Chair Name

Dr. Alexandru M.F. Tomescu

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. Paul Kenrick

Second Committee Member Affiliation

Community Member or Outside Professional

Third Committee Member Name

Dr. Anne-Laure Decombeix

Third Committee Member Affiliation

Community Member or Outside Professional

Fourth Committee Member Name

Dr. Terry Henkel

Fourth Committee Member Affiliation

HSU Faculty or Staff


Periderm, Wound response, Secondary growth, Plant anatomy, Development, Evolution, Fossil, Evo-devo, Devonian, Early tracheophyte, Euphyllophyte

Subject Categories



Periderm is a structural feature with roles in protection of inner plant tissues and wound healing. Knowledge of periderm occurrences in the fossil record and living lineages outside the seed plants is limited and its evolutionary origins remain poorly explored. Here, I review the known taxonomic distribution of canonical periderm (typical ontogenetic stage) and wound periderm (self-repair mechanism). To this sparse body of data I add new observations and experiments on living plant lineages and new occurrences from the fossil record. One of the latter, documented in the new early euphyllophyte species Nebuloxyla mikmaqiana, joins the oldest known periderm occurrences (Early Devonian), which allow me to construct a model for the development of wound-response periderm in early tracheophytes. Using a new system of quantifying periderm organization, I show that periderm represents a continuum of structural configurations predicated by the same basic process - periclinal divisions - that fall anywhere between very loosely organized (diffuse periclinal growth) and very tightly coordinated (organized periclinal growth). Wound and canonical periderms of seed plants have higher degrees of organization than those of seed-free plants, possibly due to co-option of the programs that organize their vascular cambial growth. Considered within the framework of their level of structural organization, the taxonomic and stratigraphic spread of canonical and wound periderm suggest that wound periderm may have had a single origin in euphyllophytes and canonical periderm may have originated separately in different lineages by co-option of the basic toolkit regulating wound periderm. In one evolutionary scenario, wound periderm regulators activated initially by tearing due to tensional stresses elicited by woody growth, underwent heterochronic change that switched their activation trigger from tissue tearing to the tensional stresses that precede it.

Citation Style




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