A new phylogeny of the cladoxylopsid plexus: contribution of an early cladoxylopsid from the Lower Devonian (Emsian) of Quebec

Abstract

Premise: Cladoxylopsids formed Earth's earliest forests and gave rise to the ancestors of sphenopsids and ferns. Lower Devonian (Emsian) strata of the Battery Point Formation (Quebec, Canada) contain new anatomically preserved cladoxylopsids, one of which is described in this article. To assess the phylogenetic position of this fossil and address questions of cladoxylopsid phylogeny, we conducted a comprehensive phylogenetic study. Methods: Permineralized axes were studied in serial sections using the cellulose acetate peel technique. We evaluated phylogenetic relationships among cladoxylopsids using a data set of 36 new morphological characters and 31 species, in parsimonyconstrained analyses. Results: We describe Adelocladoxis praecox gen. et sp. nov., a cladoxylopsid with small actinostelic axes bearing dichotomously branched, helically arranged ultimate appendages and fusiform sporangia. Adelocladoxis provides the oldest evidence of cladoxylopsid anatomy, including ultimate appendages and sporangia. In agreement with non-phylogenetic classification schemes, our phylogenetic analysis resolves a basal grade of iridopterids and a clade of cladoxylopsids s.s., which includes a pseudosporochnalean cladoxylopsid clade, a cladoxylalean cladoxylopsid clade, and Adelocladoxis. Conclusions: Our phylogenetic analysis illuminates aspects of tempo and mode of evolution in the cladoxylopsid plexus. Originating prior to the Emsian, cladoxylopsids reached global distribution by the Frasnian. Iridopterids and cladoxylopsids s.s. radiated in the Emsian-Eifelian. The sequence of character change recovered by our phylogeny supports a transition from actinostelic protosteles to dissected steles, associated with an increase in xylem rib number and medullation generating a central parenchymatous area.

A New Fern-like Plant Xinhangia spina Gen. et sp. Nov. from the Upper Devonian of China

“…Alternatively, the Pseudosporochnales and nonpseudosporochnaleans, as an informal group, are placed in this class [ 10 ]. The recent phylogenetic analysis regards that the cladoxylopsids sensu lato refer to the iridopteridaleans and cladoxylopsids sensu stricto , which include the pseudosporochnaleans and nonpseudopsorochnaleans [ 23 ]. In general, the iridopteridaleans refer to plants such as Anapaulia [ 24 ], Arachnoxylon [ 25 ], Asteropteris [ 26 ], Compsocradus [ 27 ], Ibyka [ 28 ], Iridopteris [ 29 ], Keraphyton [ 30 ] and, possibly, Metacladophyton [ 12 , 31 ], the pseudosporochnaleans to Calamophyton [ 32 ], Lorophyton [ 33 ], Pseudosporochnus [ 11 ] and Wattieza [ 34 ], and the nonpseudosporochnaleans to the taxa such as Cladoxylon [ 35 ], Panxia [ 36 , 37 ], Pietzschia [ 1 , 38 ], Polyxylon [ 10 ] and, possibly, Denglongia [ 13 , 14 ].…”

“…Nevertheless, its discoidal sporangia with stalks are borne laterally and closely. Metacladophyton [ 12 , 31 ] is treated as a nonpseudosporochnalean [ 23 ]. It morphologically differs from Xinhangia mainly in the whorled and decussate branches.…”

“…Denglongia [ 13 , 14 ] is placed in the cladoxylopsids s.s. , but is not allied with the nonpseudosporochnaleans or nonpseudosporochnaleans [ 23 ]. It shows clear differences with Xinhangia in the whorled branches, complex and unique fertile organs with alternate segments and actinostele.…”

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

“…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.…”