Danziella
Encyclopedia
Danziella is a genus of extinct vascular plant
s of the Early Devonian (around ). Fossils found in the Artois
region of northern France were first described as Zosterophyllum
artesianum, but a later review by Edwards showed that they did not fit the circumscription
of that genus.
region of northern France, in rocks which were originally thought to be of Pragian age (around ) but more recently have been considered to be probably of Emsian orgin (around ). Plants consisted of smooth leafless stems (axes) up to 1.5 mm wide and were at least 85 mm high. They branched at right angles. Spore-forming organs or sporangia
were borne on all sides, spaced irregularly on stalks up to 3 mm long which held them horizontally, and not forming a distinct 'spike'. Individual sporangia were elliptical in shape, around 3 mm wide by 2 mm high, splitting into two 'valves' along a line opposite to the stalks in order to release their spores. Since the sporangia were at right angles to the stem, the split was vertical.
cf. myretonianum by Corsin in 1933. In 1956 Danzé-Corsin constructed a new species, Z. artesianum to accommodate this plant, arguing that it resembled Z. llanoveranum but had its sporangia arranged in a much laxer spike. Edwards notes that since then, reviews of the genus Zosterophyllum have clarified its circumscription. All species of Zosterophyllum have a compact spike of sporangia, arranged helically with some degree of regularity. The sporangia are bivalved as in this plant, but they have short stalks which turn upwards, so that the sporangia are vertically aligned and hence split (dehisce) along a horizontal line. No other genera within the zosterophylls has the features of the French specimens, so that Edwards assigned them to a new genus, Danziella, named after Danzé-Corsin.
caledonica and Renalia
. Renalia is placed outside the zosterophylls as one of a set of sister taxa in the cladogram
for the polysporangiophyte
s which Crane et al. published in 2004. Edwards agrees that Danziella may be part of the stem group of the zosterophylls and hence the lycophyte clade, but says that it could also belong elsewhere and show convergent evolution of the mechanism by which the sporangia split to release spores.
Vascular plant
Vascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the clubmosses, Equisetum, ferns, gymnosperms and angiosperms...
s of the Early Devonian (around ). Fossils found in the Artois
Artois
Artois is a former province of northern France. Its territory has an area of around 4000 km² and a population of about one million. Its principal cities are Arras , Saint-Omer, Lens and Béthune.-Location:...
region of northern France were first described as Zosterophyllum
Zosterophyllum
Zosterophyllum was a genus of Silurian-Devonian land plant with branching axes.Some species have been transferred to other genera:* Z. artesianum to Danziella artesiana* Z. contiguum to Demersatheca contigua...
artesianum, but a later review by Edwards showed that they did not fit the circumscription
Circumscription (taxonomy)
In taxonomy, circumscription is the definition of the limits of a taxonomic group of organisms. One goal of taxonomy is to achieve a stable circumscription for every taxonomic group. Achieving stability can be simple or difficult....
of that genus.
Description
Compressed fossils were found in the ArtoisArtois
Artois is a former province of northern France. Its territory has an area of around 4000 km² and a population of about one million. Its principal cities are Arras , Saint-Omer, Lens and Béthune.-Location:...
region of northern France, in rocks which were originally thought to be of Pragian age (around ) but more recently have been considered to be probably of Emsian orgin (around ). Plants consisted of smooth leafless stems (axes) up to 1.5 mm wide and were at least 85 mm high. They branched at right angles. Spore-forming organs or sporangia
Sporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...
were borne on all sides, spaced irregularly on stalks up to 3 mm long which held them horizontally, and not forming a distinct 'spike'. Individual sporangia were elliptical in shape, around 3 mm wide by 2 mm high, splitting into two 'valves' along a line opposite to the stalks in order to release their spores. Since the sporangia were at right angles to the stem, the split was vertical.
Taxonomy
Specimens were first attributed to ZosterophyllumZosterophyllum
Zosterophyllum was a genus of Silurian-Devonian land plant with branching axes.Some species have been transferred to other genera:* Z. artesianum to Danziella artesiana* Z. contiguum to Demersatheca contigua...
cf. myretonianum by Corsin in 1933. In 1956 Danzé-Corsin constructed a new species, Z. artesianum to accommodate this plant, arguing that it resembled Z. llanoveranum but had its sporangia arranged in a much laxer spike. Edwards notes that since then, reviews of the genus Zosterophyllum have clarified its circumscription. All species of Zosterophyllum have a compact spike of sporangia, arranged helically with some degree of regularity. The sporangia are bivalved as in this plant, but they have short stalks which turn upwards, so that the sporangia are vertically aligned and hence split (dehisce) along a horizontal line. No other genera within the zosterophylls has the features of the French specimens, so that Edwards assigned them to a new genus, Danziella, named after Danzé-Corsin.
Phylogeny
Edwards considers the placement of Danziella to be uncertain. It has a simpler organization than most of the genera assigned to the zosterophylls, somewhat resembling taxa such as CooksoniaCooksonia
Cooksonia is an extinct grouping of primitive land plants. The earliest Cooksonia date from the middle of the Silurian ; the group continues to be an important component of the flora until the Early Devonian, a total time span of...
caledonica and Renalia
Renalia
Renalia is a genus of extinct vascular plants from the Early Devonian . It was first described in 1976 from compressed fossils in the Battery Point Formation .-Description:...
. Renalia is placed outside the zosterophylls as one of a set of sister taxa in the cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
for the polysporangiophyte
Polysporangiophyte
Polysporangiophytes, also called polysporangiates or more formally Polysporangiophyta, are plants in which the spore-bearing generation has a structure of branching stems terminating in sporangia...
s which Crane et al. published in 2004. Edwards agrees that Danziella may be part of the stem group of the zosterophylls and hence the lycophyte clade, but says that it could also belong elsewhere and show convergent evolution of the mechanism by which the sporangia split to release spores.