Abstract

The morphology of plant fossils from the Rhynie chert has generated longstanding questions about vascular plant shoot and leaf evolution, for instance, which morphologies were ancestral within land plants, when did vascular plants first arise and did leaves have multiple evolutionary origins? Recent advances combining insights from molecular phylogeny, palaeobotany and evo–devo research address these questions and suggest the sequence of morphological innovation during vascular plant shoot and leaf evolution. The evidence pinpoints testable developmental and genetic hypotheses relating to the origin of branching and indeterminate shoot architectures prior to the evolution of leaves, and demonstrates underestimation of polyphyly in the evolution of leaves from branching forms in ‘telome theory’ hypotheses of leaf evolution. This review discusses fossil, developmental and genetic evidence relating to the evolution of vascular plant shoots and leaves in a phylogenetic framework.This article is part of a discussion meeting issue ‘The Rhynie cherts: our earliest terrestrial ecosystem revisited’.

Highlights

  • Today’s biota includes ca 375 000 species of vascular plant that generate over 90% of terrestrial productivity, and variation in shoot and leaf form are major components of vascular plant biodiversity [1 –3]

  • The earliest land plants arose about 470 million years ago and are evidenced in the fossil record as spores or spore masses [4,5,6,7]. These plants lacked shoots and leaves, instead having tiny fertile axes that entered reproductive development straight away or elaborated a small axis terminating in sporangium formation [8,9,10], and similar forms remain evident among living bryophyte relatives of the earliest land plants, which comprise ca 20 000 species [1]

  • Many pro-vascular and early vascular plant forms in the fossil record look very different to modern vascular plants and exhibit traits that suggest stepwise changes in form from a bryophyte-like evolutionary starting point [9,10,11,18]

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Summary

Introduction

Today’s biota includes ca 375 000 species of vascular plant that generate over 90% of terrestrial productivity, and variation in shoot and leaf form are major components of vascular plant biodiversity [1 –3]. The earliest land plants arose about 470 million years ago and are evidenced in the fossil record as spores or spore masses [4,5,6,7]. These plants lacked shoots and leaves, instead having tiny fertile axes that entered reproductive development straight away or elaborated a small axis terminating in sporangium formation [8,9,10], and similar forms remain evident among living bryophyte relatives of the earliest land plants, which comprise ca 20 000 species [1]. Over 100 years, e.g. [19,20], and the new tools and fossil evidence that we have at our disposal offer the possibility to generate knowledge that will fundamentally advance our understanding of vascular plant form and evolution [10,21,22,23]

Identifying the direction of evolutionary trait change
Findings
Morphological transitions during the origin of vascular plant shoot systems
Full Text
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