Taxon sampling and alternative hypotheses of relationships in the euphyllophyte plexus that gave rise to seed plants: insights from an Early Devonian radiatopsid

Abstract

Summary An abrupt transition in the fossil record separates Early Devonian euphyllophytes with a simple structure from a broad diversity of structurally complex Middle–Late Devonian plants. Morphological evolution and phylogeny across this transition are poorly understood due to incomplete sampling of the fossil record. We document a new Early Devonian radiatopsid and integrate it in analyses addressing euphyllophyte relationships. Anatomically preserved Emsian fossils (402–394 Ma) from the Battery Point Formation (Gaspé, Quebec, Canada) are studied in serial sections. The phylogenetic analysis is based on a matrix of 31 taxa and 50 characters emphasising vegetative morphology (41 discrete, nine continuous). The new plant, Kenrickia bivena gen. et sp. nov., is one of very few structurally complex euphyllophytes documented in the Early Devonian. Inclusion of Kenrickia overturns previously established phylogenetic relationships among Radiatopses, reiterating the need for increased density of Early Devonian taxon sampling. Kenrickia is recovered as the sister lineage to all other radiatopsids, a clade in which paraphyletic Stenokoleales led to a lignophyte clade where archaeopterids and seed plants fall into sister clades. Our results shed light on early euphyllophyte relationships and evolution, indicating early exploration of structural complexity by multiple lineages and reiterating the potential of a single origin of secondary growth in euphyllophytes.

Complex wound response mechanisms and phellogen evolution – insights from Early Devonian euphyllophytes

“…Banks and Colthart assigned the wounded axes to trimerophytes and possibly Psilophyton , but we now recognize that one of the axes (in fig. 9 of Banks & Colthart, 1993) belongs to Kenrickia (Toledo et al ., 2021). Positionally, the Banks and Colthart wound periderms fall into two categories: (1) periderm developed beneath the outer cortical layers; and (2) periderm that fills surface wounds.…”

“…The fossil flora of the Battery Point Formation, studied ever since the mid‐19 th century (Dawson, 1859), has recently yielded a diversity of permineralized taxa that contribute to the understanding of early tracheophyte anatomy, phylogeny, and development (Bickner & Tomescu, 2019; Durieux et al ., 2021; Pfeiler & Tomescu, 2021; Toledo et al ., 2021; Tomescu & McQueen, 2022). Secondary growth, a major structural innovation in plants until recently thought to have evolved in the Middle Devonian, has been shown to have arisen much earlier (Gerrienne et al ., 2011) and has been documented in several plant types of the Gaspé flora that produced secondary xylem (Hoffman & Tomescu, 2013; Pfeiler & Tomescu, 2021; Toledo et al ., 2021).…”

Mosaic assembly of regulatory programs for vascular cambial growth: a view from the Early Devonian

“…The beginnings of this consequential radiation, in the Early Devonian, are poorly documented, especially in terms of plant structure and development. Thus, it is notable that several recent fossil discoveries have revealed previously unrecognized anatomical diversity among Early Devonian euphyllophytes (Gerrienne et al ., 2011; Hoffman & Tomescu, 2013; Strullu‐Derrien et al ., 2014; Gensel, 2018; Bickner & Tomescu, 2019; Durieux et al ., 2021; Pfeiler & Tomescu, 2021; Toledo et al ., 2021). The new plants inform hypotheses of phylogenetic relationships of basal tracheophytes and reveal unexpected complexity (Niklas & Crepet, 2020; Durieux et al ., 2021; Toledo et al ., 2021) in the early stages of the tracheophyte radiation.…”

“…Thus, it is notable that several recent fossil discoveries have revealed previously unrecognized anatomical diversity among Early Devonian euphyllophytes (Gerrienne et al ., 2011; Hoffman & Tomescu, 2013; Strullu‐Derrien et al ., 2014; Gensel, 2018; Bickner & Tomescu, 2019; Durieux et al ., 2021; Pfeiler & Tomescu, 2021; Toledo et al ., 2021). The new plants inform hypotheses of phylogenetic relationships of basal tracheophytes and reveal unexpected complexity (Niklas & Crepet, 2020; Durieux et al ., 2021; Toledo et al ., 2021) in the early stages of the tracheophyte radiation. A prime example of a character that contributes to structural diversity and complexity is secondary growth from a vascular cambium, which produces secondary xylem (wood).…”

Divergent evolutionary trajectories of bryophytes and tracheophytes from a complex common ancestor of land plants

“…Thus, a minimum age constraint of 199.5 ± 0.3 Ma was proposed[81]. Kenrickia bivena [Axis in slab 557820-5, Smithsonian Institution, NMNH] from the Battery Point Formation (Early Devonian), Quebec, Canada Phylogenetic justification: A cladistic analysis by Toledo et al[82] of 50 morphological characters supported Kenrickia as sister to all other radiatopsids, a lineage within euphyllophytes and outgroup to remaining progymnosperms and seed plants. Material was collected from the south shore of Gaspé Bay, near Douglastown, QC, Canada.…”