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Updated: Jun 25, 2026
09:38
Collection and Analysis of Arabidopsis Phloem Exudates Using the EDTA-facilitated Method
Published on: October 23, 2013
Phloem evolved gradually and asynchronously to xylem in early vascular plants
Laura M Cooper1, Alexander J Hetherington2
1Institute of Molecular Plant Sciences, University of Edinburgh, Max Born Crescent, Edinburgh EH9 3BF, UK.
Current Biology : CB
|June 23, 2026
Summary
Early vascular plants had food-conducting cells (FCCs), not true phloem, with features evolving gradually. This study reveals early plant vasculature and the origins of phloem in ancient fossils.
Area of Science:
- Paleobotany
- Evolutionary Biology
- Plant Anatomy
Background:
- The evolution of xylem and phloem enabled long-distance transport in land plants.
- The fossil record for phloem is limited compared to xylem due to preservation biases.
- The evolutionary origins of vascular tissues remain unclear.
Purpose of the Study:
- To investigate the "phloem-like" tissues in exceptionally preserved early land plants.
- To overcome limitations in the fossil record for understanding vascular tissue evolution.
- To characterize the histological differences between early food-conducting tissues and extant phloem.
Main Methods:
- Re-description of exceptionally preserved "phloem-like" tissues from the 407-million-year-old Rhynie chert.
- Histological analysis of fossil plant anatomy, including cell diameter and presence of pericycle.
- Identification of putative sieve pores in fossilized food-conducting cells.
Main Results:
- The "phloem-like" tissue in Rhynie chert plants, identified as food-conducting cells (FCCs), differs significantly from extant phloem.
- Early vascular plants lacked a pericycle, and FCCs were larger than extant phloem cells.
- Putative sieve pores were identified in *Asteroxylon mackiei* FCCs, representing the earliest fossil evidence of these structures.
Conclusions:
- Early vascular plants likely lacked true phloem, possessing FCCs instead.
- Phloem features evolved gradually within FCCs, asynchronously with xylem evolution.
- This study provides insights into the early evolution of plant vasculature and food transport mechanisms.
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