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Philos Trans R Soc Lond B Biol Sci. 2000 June 29; 355(1398): 857–868.
PMCID: PMC1692781

The origin and early evolution of tracheids in vascular plants: integration of palaeobotanical and neobotanical data.


Although there is clear evidence for the establishment of terrestrial plant life by the end of the Ordovician, the fossil record indicates that land plants remained extremely small and structurally simple until the Late Silurian. Among the events associated with this first major radiation of land plants is the evolution of tracheids, complex water-conducting cells defined by the presence of lignified secondary cell wall thickenings. Recent palaeobotanical analyses indicate that Early Devonian tracheids appear to possess secondary cell wall thickenings composed of two distinct layers: a degradation-prone layer adjacent to the primary cell wall and a degradation-resistant (possibly lignified) layer next to the cell lumen. In order to understand better the early evolution of tracheids, developmental and comparative studies of key basal (and potentially plesiomorphic) extant vascular plants have been initiated. Ultrastructural analysis and enzyme degradation studies of wall structure (to approximate diagenetic alterations of fossil tracheid structure) have been conducted on basal members of each of the two major clades of extant vascular plants: Huperzia (Lycophytina) and Equisetum (Euphyllophytina. This research demonstrates that secondary cell walls of extant basal vascular plants include a degradation-prone layer ('template layer') and a degradation-resistant layer ('resistant layer'). This pattern of secondary cell wall formation in the water-conducting cells of extant vascular plants matches the pattern of wall thickenings in the tracheids of early fossil vascular plants and provides a key evolutionary link between tracheids of living vascular plants and those of their earliest fossil ancestors. Further studies of tracheid development and structure among basal extant vascular plants will lead to a more precise reconstruction of the early evolution of water-conducting tissues in land plants, and will add to the current limited knowledge of spatial, temporal and cytochemical aspects of cell wall formation in tracheary elements of vascular plants.

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Selected References

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  • Alberch P, Blanco MJ. Evolutionary patterns in ontogenetic transformation: from laws to regularities. Int J Dev Biol. 1996 Aug;40(4):845–858. [PubMed]
  • Ros Barceló A. Lignification in plant cell walls. Int Rev Cytol. 1997;176:87–132. [PubMed]
  • Carlquist S, Schneider EL. Sem studies on vessels in ferns. 12. Marattiaceae, with comments on vessel patterns in eusporangiate ferns. Am J Bot. 1999 Apr;86(4):457–464. [PubMed]
  • Knoll AH. Proterozoic and early Cambrian protists: evidence for accelerating evolutionary tempo. Proc Natl Acad Sci U S A. 1994 Jul 19;91(15):6743–6750. [PubMed]
  • Knoll AH, Niklas KJ. Adaptation, plant evolution, and the fossil record. Rev Palaeobot Palynol. 1987;50:127–149. [PubMed]
  • Manhart JR. Phylogenetic analysis of green plant rbcL sequences. Mol Phylogenet Evol. 1994 Jun;3(2):114–127. [PubMed]
  • Qiu YL, Cho Y, Cox JC, Palmer JD. The gain of three mitochondrial introns identifies liverworts as the earliest land plants. Nature. 1998 Aug 13;394(6694):671–674. [PubMed]
  • Raubeson LA, Jansen RK. Chloroplast DNA evidence on the ancient evolutionary split in vascular land plants. Science. 1992 Mar 27;255(5052):1697–1699. [PubMed]

Articles from Philosophical Transactions of the Royal Society B: Biological Sciences are provided here courtesy of The Royal Society