Abstract Detail

PhyloCode 2020: Naming the Tree of Life

Doyle, James [1].

Value of phylogenetic nomenclature in investigating relationships of fossil and extant seed plants and angiosperms.

Phylogenetic nomenclature provides an improved framework for discussions of relationships of fossils and extant taxa. The PhyloCode recommends application of familiar names to crown clades; i.e., the most recent common ancestor (MRCA) of all living members of a line and its derivatives, living and fossil. These names have the advantage of corresponding to clades inferred from molecular analyses. Such definitions exclude stem relatives; i.e., fossil taxa attached to the stem lineage between the crown clade and its common ancestor with the most closely related crown clade. The total clade, which includes the crown clade and all its stem relatives, can be designated by adding the prefix Pan- to the crown clade name. Apomorphy-based names designate clades derived from the first ancestor with a particular homologous derived feature. When this apomorphy is etymologically reflected in the name of the largest included crown clade, the apomorphy-based name can consist of the crown clade name with the prefix Apo-. This scheme can clarify cases where typological definitions based on “defining” characters lead to confusion. The name Spermatophyta designates crown clade seed plants, which do not include Late Devonian and Carboniferous hydrasperman, lyginopterid, and medullosan “seed ferns.” However, these stem relatives belong to the apomorphy-based clade Apo-Spermatophyta (from the first ancestor with seeds). The total clade Pan-Spermatophyta includes fossils down to the MRCA of seed plants and monilophytes. This may be nearly equivalent to the apomorphy-based clade Lignophyta (from the first ancestor with a bifacial cambium), which includes “progymnosperms” such as Archaeopteris. The name Angiospermae designates the crown clade derived from the MRCA of living angiosperms, whereas Apo-Angiospermae also include any stem relatives with a carpel homologous with that in Angiospermae. Such stem relatives have not been conclusively identified; their recognition would not affect the content of Angiospermae. Fossils with enclosed seeds are not by definition Angiospermae or Apo-Angiospermae; identifying them as such requires evidence that the enclosing structure is homologous with the carpel of living angiosperms, based on morphological correspondence and phylogenetic analysis using all available characters. Pan-Angiospermae include typologically gymnospermous fossils that are more closely related to angiosperms than they are to any extant gymnosperms. Various analyses have proposed glossopterids, Bennettitales, Caytonia, and Petriellaea as such fossils; determining which if any of these are indeed Pan-Angiospermae is essential for understanding the origin of typical angiosperm structures such as the carpel.

1 - University Of California Davis, DEPT OF EVOL & ECOLOGY, One Shields Avenue, Davis, CA, 95616, United States

phylogenetic nomenclature
seed plants

Presentation Type: Colloquium Presentations
Abstract ID:537
Candidate for Awards:None

Copyright © 2000-2021, Botanical Society of America. All rights reserved