Sawdonia

Sawdonia
Temporal range: Upper Silurian–Lower Carboniferous
Sawdonia ornata
Sawdonia ornata
Scientific classification
Division:Tracheophytes
Class:†Zosterophyllopsida
Order:†Sawdoniales
Family:†Sawdoniaceae
Genus:†Sawdonia
Francis Hueber- 1971
Species
  • †''Sawdonia ornata''
  • †''Sawdonia acanthotheca''

Sawdonia is a member of the Sawdoniaceae family, which contains the earliest vascular land plants. These plants are best recognized by the large amount of spikes (enations) covering the plant. These are vascular plants that do not have vascular systems in their enations. The first species of this genus (Sawdonia Ornata) was described in 1859 by Sir J. William Dawson and, was originally attributed to the Psilophyton genus. He named this plant Psilophyton Princeps. In 1971 Francis Hueber proposed a new genus for this species due to its "Divergent technical characters from the generic description for Psilophyton."[1] The holotype used for description is Dawson Collection Number 48, pro parte, Museum Specimen Number 3243. (See Dawson 1871, Plate IX, fig 101.) Sir J. William Dawson Collection, Peter Redpath Museum, McGill University, Montreal, Qu6bec, Canada.[1]

Morphology

These plants are described by Hueber as having monopodially branched stems, that are unridged, spinous and circinately tipped. The sporangia are described as round in abaxial view, and oval in lateral view. These sporangia are formed laterally and singular on short stalks. The sporangium split along convex margins into equal valves in a trilete fashion. The spines are tapered and pointed lower on the plant but form loose spikes at end of the plant. The sporangium split along convex margins into equal valves in a trilete fashion.The xylem are just one solid strand. The epidermal cells have cuticular papillae. There are stomata located on the on stem but not on spine surfaces.[1]

Sawdonia is defined by Francis Hueber in his 1971 paper as follows:

  1. Having stems up to 5mm in diameter without measuring the spikes
  2. Multi cellular spines measuring 0.5-1.8 mm at the base, reaching 0.5-3.9mm long, with a density range of 4 to 45 per cm of stem
  3. Sporangia: 3-3.5 mm in diameter, with stalks 0.5-0.75 mm long and 1-1.25 mm wide
  4. A present Vascular strand
  5. Spores: round to sub-triangular, 54-64 um, trilete simple structure
  6. An oval xylem strand when viewed in cross section .074x0.34 mm in diameter
  7. Trachieds that have a helical scalariform
  8. Stomata 39-72 um long, 17-34 um wide, with parallel elongation in regards to the axis of the stem, with a thickened outer wall of guard cells[1]

Taxonomy and classification

Division Tracheophyta

Subdivision Zosterophyllophytina

Order Sawdoniales[2]

Family Sawdoniaceae [2]

Genus Sawdonia

Species

  • Sawdonia ornata[3]
  • Sawdonia acanthotheca[4]
  • Sawdonia curtsipa (disputed)[5]

Range

Sawdonia had an extremely broad range, with many specimens found in Canada, England and Scotland. There have even been a species that has been found across China, that might fall under the Sawdonia genus.

References

  1. 1 2 3 4 Hueber, Francis M (1971). "Sawdonia Ornata: A New Name for Psilophyton princeps var. Ornatum". Taxon. 20 (4): 641–2. doi:10.2307/1218284. JSTOR 1218284.
  2. 1 2 Kenrick, Paul, and Peter R. Crane. The Origin and Early Diversification of Land Plants: a Cladistic Study. Smithsonian Inst. Press, 1997.
  3. ↑ Gensel, Patricia G; Berry, Christopher M (2016). "Sporangial Morphology of the Early Devonian Zosterophyll Sawdonia ornata from the Type Locality (Gaspé)". International Journal of Plant Sciences. 177 (7): 618–32. doi:10.1086/687301.
  4. ↑ Gensel, Patricia G; Andrews, Henry N; Forbes, William H (1975). "A New Species of Sawdonia with Notes on the Origin of Microphylls and Lateral Sporangia". Botanical Gazette. 136 (1): 50–62. doi:10.1086/336782.
  5. ↑ Xu, Hong-He (2011). "Re-examination of specimens attributed to Sawdonia curstipa Wang and Hao (zosterophyll) from the Middle Devonian of Xinjiang, China". Palaeoworld. 20 (4): 357–61. doi:10.1016/j.palwor.2011.06.003.
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