A Simple Type of Wood in Two Early Devonian Plants

Abstract

The advent of wood (secondary xylem) is a major event of the Paleozoic Era, facilitating the evolution of large perennial plants. The first steps of wood evolution are unknown. We describe two small Early Devonian (407 to 397 million years ago) plants with secondary xylem including simple rays. Their wood currently represents the earliest evidence of secondary growth in plants. The small size of the plants and the presence of thick-walled cortical cells confirm that wood early evolution was driven by hydraulic constraints rather than by the necessity of mechanical support for increasing height. The plants described here are most probably precursors of lignophytes.

The Structure and Function of Xylem in Seed-Free Vascular Plants: An Evolutionary Perspective

“…Fossils show that tracheid diameter increased by an order of magnitude during the Devonian from the 8 μm tracheids of the primitive Cooksonia to the 140 μm metaxylem conduits of Stenomylon primaevum , an early Carboniferous seed fern (Niklas 1985 ). Although early vascular plants such as Rhynia and Asteroxylon were herbaceous, the recent identifi cation of true secondary xylem in putative relatives of Psilophyton and Armoricaphyton suggests that this trait evolved much earlier than originally thought ( Gerrienne et al 2011 ;Strullu-Derrien et al 2014 ). It appears that Psilophyton had a bifacial vascular cambium in which cell initials divide both radially and tangentially.…”

“…Prior to the discovery of true secondary xylem in Psilophyton , the progymnosperms were thought to represent the earliest known class of plants with true wood derived from a bifacial cambium (Gerrienne et al 2011 ). This group of plants possessed the unusual combination of coniferous, pycnoxylic wood with a canopy comprising free-sporing foliage, superfi cially similar to those of ferns (Beck 1970 ;Taylor et al 2009 ).…”

Earliest land plants created modern levels of atmospheric oxygen

“…The Carboniferous-Permian peak in coal production has often been attributed to the evolution of lignin synthesis and a lag before the evolution of fungal degradation of lignin (23), but recent work has questioned this (24). Earlier plants possessed lignified "woody" tissue (25), with precursor structures existing in marine algae before the transition to land (26), and lignin-degrading fungi potentially present before the Carboniferous (24). Carboniferous coals are not dominated by lignin; instead, their accumulation was controlled by a combination of climate and tectonics supporting the creation and sedimentary preservation of peat bogs (24,27).…”

A Review of Proterozoic to Early Paleozoic Lithotectonic Terranes in New Brunswick, Canada and their Tectonic Evolution during Penobscot, Taconic, Salinic and Acadian Orogenesis

“…The Lower Devonian (late Emsian) Campbellton Formation is a sequence of terrestrial conglomerate, sandstone, and mudstone rich in plant and fish fossils. It unconformably overlies volcanic rocks of the Dalhousie Group along the Bay of Chaleur (Dineley and Williams 1968;Andrews et al 1974Andrews et al , 1975Gensel 1982;Trant and Gensel 1985;Richardson and McGregor 1986;Gensel et al 1991;Johnson and Gensel 1992;Miller 1996;Shear et al 1996;Miller et al 2003;Wilson et al 2005;Burrow et al 2008;Turner and Miller 2008;Gerrienne et al 2011).…”