A Middle Devonian Callixylon (Archaeopteridales) from Ronquières, Belgium

Abstract

A permineralized Callixylon trunk is reported from Ronquières, a mid to late Givetian (Middle Devonian) locality from Belgium. The specimen consists of an 80 cm long trunk adpression whose central area is preserved as a pyrite permineralization. The pyritized area is composed of a eustele surrounded by secondary xylem. Tracheids show radially aligned groups of pits separated by unpitted regions on the radial walls of tracheids. The specimen belongs to a group of species characterized by a predominance of uniseriate rays and the lack of ray tracheids. This Callixylon specimen is one of the earliest representatives of the genus. It coexists at the locality with large cladoxylopsids and provides direct evidence that the tree habit had evolved in the archaeopteridalean progymnosperms by the Givetian.

A Callixylon (Archaeopteridales, Progymnospermopsida) trunk with preserved secondary phloem from the Late Devonian of Morocco

“…Among the progymnosperms, the Archaeopteridales are of particular interest because they are among the oldest plants to have reached the tree habit during the Middle Devonian (e.g., see Meyer‐Berthaud and Decombeix, 2007; Meyer‐Berthaud et al, 2010; Cornet et al, 2012). From an ecological point of view, the abundance and worldwide distribution of archaeopteridalean fossils during the Late Devonian indicate that this group was a major component of ecosystems worldwide until their extinction around the Devonian/Carboniferous boundary (Beerbower et al, 1992).…”

Callixylon wendtiisp. nov., a new species of archaeopteridalean progymnosperm from the Late Devonian of Anti-Atlas, Morocco

“…The possession of a heterogeneous pith comprised of scattered thick-walled cells is an ancient character of the eustelic lignophytes, reported as early as the Givetian in Callixylon (Cornet et al 2012). The arrangement of sclerotic cells in large clusters or nests, however, was not recorded in the pith of any Devonian taxa prior to the present paper.…”

An overview of the hydraulic systems in early land plants

“…The first forest ecosystems evolved by the middle part of the Devonian Period, and they were populated by arborescent plants belonging to several major lineages (Bateman et al 1998;Gensel & Edwards 2001;Stein et al 2007;Gensel 2008;Meyer-Berthaud et al 2010;Cornet et al 2012;Stein et al 2012;Giesen & Berry 2013). Arborescence is known to have evolved in plants independently in many different groups, and a variety of biomechanical strategies were employed (Mosbrugger 1990;Niklas 1997;Rothwell et al 2008;Pittermann 2010).…”