Sawdonia is an extinct genus of early

vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They al ...

s, known from the

Upper Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

to the

Lower Carboniferous Lower may refer to: *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is situated about five miles south west of Dursley, eight ...

(). ''Sawdonia'' is best recognized by the large number of spikes (

enation Enations are scaly leaflike structures, differing from leaves in their lack of vascular tissue. They are created by some leaf diseases and occur normally on ''Psilotum''. Enations are also found on some early plants such as ''Rhynia'', where the ...

s) 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 genus ''

Psilophyton ''Psilophyton'' is a genus (biology), genus of extinct vascular plants. Described in 1859, it was one of the first fossil plants to be found which was of Devonian age (about ). Specimens have been found in northern Maine, USA; Gaspé Bay, Queb ...

''. 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''." 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, Quebec, Canada.

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 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. ''Sawdonia'' is defined by Francis Hueber in his 1971 paper as follows: # Having stems up to 5 mm in diameter without measuring the spikes # 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 # Sporangia: 3-3.5 mm in diameter, with stalks 0.5-0.75 mm long and 1-1.25 mm wide # A present Vascular strand # Spores: round to sub-triangular, 54-64 um,

trilete In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

simple structure # An oval xylem strand when viewed in cross section .074x0.34 mm in diameter # Trachieds that have a helical scalariform # 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

Taxonomy

Classification

There is agreement that ''Sawdonia'' was a

zosterophyll The zosterophylls are a group of extinct land plants that first appeared in the Silurian period. The taxon was first established by Banks in 1968 as the subdivision Zosterophyllophytina; they have since also been treated as the division Zosteroph ...

– a group of plants on the line of evolution leading to the modern lycopodiopsids. In their 1997

cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

study, Kenrick and Crane placed ''Sawdonia'' in the family

Sawdoniaceae Sawdoniaceae is a family of extinct zosterophylls. The zosterophylls were among the first vascular plants in the fossil record, and are considered to share an ancestor with the living lycophytes. The family is recognized by some sources, and pl ...

, order

Sawdoniales The Sawdoniales are an order or plesion of extinct zosterophylls. The zosterophylls were among the first vascular plants in the fossil record, and share an ancestor with the living lycophytes. The group has been divided up in various ways. In t ...

.Kenrick, Paul, and Peter R. Crane. ''The Origin and Early Diversification of Land Plants: a Cladistic Study''. Smithsonian Inst. Press, 1997. An alternative view places the genus in the family

Gosslingiaceae Gosslingiaceae is a family of extinct zosterophylls. The zosterophylls were among the first vascular plants in the fossil record, and are considered to share an ancestor with the living lycophytes. The family is variously placed in the order Sa ...

, order

Gosslingiales Gosslingiales is an order of extinct zosterophylls. The zosterophylls were among the first vascular plants in the fossil record, and share an ancestor with the living lycophytes. The group has been divided up in various ways. Hao and Xue in 20 ...

Species

*''Sawdonia ornata'' *''Sawdonia acanthotheca'' *''Sawdonia curstipa'' (disputed)

Range

''Sawdonia'' had an extremely broad range, with many specimens found in

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

(

Battery Point Formation The Battery Point Formation is a geologic formation in Quebec. It preserves fossils dating back to the early Emsian to early Eifelian the lower Devonian period. Description A part of the Gaspé Sandstones, the Battery Point Formation is believed ...

Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in th ...

(

Campo Chico Formation Campo may refer to: Places ;Cameroon * Campo, Cameroon, in the South Province ;Equatorial Guinea * Río Campo, in the Litoral Province ;France * Campo, Corse-du-Sud, a commune on the island of Corsica ;Italy * Campo P.G., a World War II prison ...

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

and

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...

(

Strathmore Group The Strathmore Group is a Devonian lithostratigraphic group (a sequence of rock strata) in central Scotland. Its sandstones are interbedded with siltstones which interfinger with conglomerates. It is encountered from Arran in the west across th ...

). There have even been a species that has been found across China, that might fall under the Sawdonia genus.

References

{{Taxonbar, from=Q2228280 Paleozoic life of Ontario Paleozoic life of Quebec Zosterophylls Prehistoric lycophyte genera