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Derived zosterophylls
Derived zosterophylls
A group of leafless plants with upright branching and uncoiling new shoots (circinate growth). These coiled shoots would be called fiddleheads in ferns, and this looks to be convergent evolution between these groups. Some of these plants have spines scattered along the stem, and spore cases in two vertical rows. Some of the members, such as Bathurstia †, had roots, representing some of the oldest known for land plants.
Ecology & Form
Ecology & Form
Sporophyte (spore-bearing) phase
Sporophyte (spore-bearing) phase
Stems
Stems
~30cm tall
Pseudomonopodial growth, but distal axes could be isotomously branched
Circinate tips with fiddleheads
Leaves
Leaves
Leafless
Papillae and spines on stems
Roots
Roots
Some members had rooting organs arising from the main aerial axes
These represent some of the oldest known roots in land plants
Reproduction
Reproduction
Sporangia isovalvate (calm-like) dehiscence
Kidney-shaped sporangia
Sporangia arranged in 2 vertical rows, and attached laterally on the stem
Gametophyte (gamete-bearing) phase
Gametophyte (gamete-bearing) phase
There are gametophytes preserved in the Rhynie Chert that were associated with zosterophylls
Kidstonophyton discoides † was a male gametophyte of a zosterophyll, probably Nothia (Remy et al., 1993)
Geologic Age
Geologic Age
Classification
Classification
└Sawdoniales †
Bathurstia denticulata †
Bathurstia denticulata †
Hueber, 1972; Kotyk & Basinger, 2000
Pragian of Bathurst Island, Canadian Arctic Archipelago
Poorly preserved spike of sporangia found in the Ludlow (Kotyk et al., 2002)
Scrambler of about 30 cm in height.
Stems bear short, shelf-like emergences in two rows, and branch isotomously, although sparsely.
Earliest known rooting organs (Pragian) arise from the main aerial axes, although they are also associated with small, subordinate shoots interpreted as plantlets.
They lack some of the features of true roots
Numerous specimens are fertile, with sporangia borne in dense terminal spikes.
Spikes include two rows of overlapping, discoid sporangia.
This plant has some resemblance to Serrulacaulis, Barinophytes, and the Gosslingia.
Above: A reconstruction of Bathurstia denticulata † showing roots, upright axes, and sporangia (Kotyk & Basinger, 2000, Fig 18)
Crenaticaulis †
Crenaticaulis †
Slender, pseudomonopodial and dichotomously branched
Bore opposite to subopposite sporangia along the stem
Two rows of prominent, multicellular teeth on opposite sides of the terete axis
Epidermal cells were either narrow and elongate parallel to the stem or short with a papillate outer tangential wall
Axillary tubercles were present on one side of the stem near lateral branches
Some tubercles bore remnants of branches
It is suggested that the so-called axillary tubercles were scars of rhizophores like those in the modern genus Selaginella
Sporangia dehisced along their distal margins into two unequal halves.
Xylem stele was elliptical in transverse section and maturation was exarch.
Tracheids were chiefly scalariform.
Above: A compression fossil of Crenaticaulis †
Deheubarthia splendens †
Deheubarthia splendens †
Edwards et al., 1989
Early Devonian (Pragian) of UK
Axes at least 30 cm tall with spines
Branching is pseudomonopodial and planar, with subaxillary branches
Above: A reconstruction of Deheubarthia splendens † axis with axillary tubercle branch from Kenrick and Crane, 1997
Above: A reconstruction of Deheubarthia splendens † from Kenrick and Crane, 1997
Faironella valentula †
Faironella valentula †
Early Emsian Age of the Wepion Formation, Belgium
The spiny axes of the plant are both isotomously and anisotomously branched
K-branching is frequent
Some specimens show a very spiny short axis on the abaxial side of the smaller axis resulting from anisotomous branching
The fertile organs are borne laterally and loosely arranged in two vertices
Right: A reconstruction of Faironella valentula †
Forania plegiospinosa †
Forania plegiospinosa †
Early Devonian plant from New Brunswick, Canada
Decumbent plant, bearing stout, mostly retrorsely curved, spine-like emergences arranged in two rows along the axes, variable modes of branching, circinately coiled axes, lateral buds, and sparsely scattered, circular to reniform lateral sporangia
Cuticular features of this species include polygonal epidermal cells and anomocytic sporangia
This plant provides the first documented evidence of stomata on emergences
The presence of stomata on the bases of large emergences suggests that emergence volume is a factor in stomatal location and development
Sporangia are solitary rather than in two rows
Above: A reconstruction of Forania plegiospinosa † from Fig 7 of Jensen & Gensel, 2013
Gosslingia †
Gosslingia †
Stems
Pseudomonopodial with isotomous distal tips
Circinate tips
Subordinate axes below dichotomies
Leafless
No spines or enations
Reproductive Structures
Ear-shaped attachment of sporangia to stems
G. americana
Tanner, 1982
G. breconensis
Heard, 1927
G. cordiformis
Schweitzer, 1979
Right: A reconstruction of Gosslingia †
Kidstonophyton discoides †
Kidstonophyton discoides †
Early Devonian of Scotland in the Rhynie Chert
The axes are 1.8-2.3 mm wide and are preserved for a length of at least 1 cm (Remy et al., 1993)
They are covered with elongate-fusiform emergences that appear pyramidal in lateral view
The aerial axis of the free-living gametophyte shows the same general morphology and anatomy as that of the sporophyte, including vascular tissue
However, the distal end terminates in a distinct cup or disc with tubular projections that bear the antheridia
This is probably the male gametophyte phase of Nothia aphylla † (Remy et al., 1993)
Konioria andrychoviensis †
Konioria andrychoviensis †
Lower Devonian (Emsian) in the Bielsko-Andrychow area of the Polish Western Carpathians
Dichotomous axes, covered with long subulate spines on proximal portions, and short triangular spines on their distal portions
Apices of axes form hooks
Axes show 1-4 longitudinal wings
Sporangia are reniform to rounded, born singly at dichotomies
Anatomy exhibits a central exarch strand with scalariform tracheids and a hypodermis
Above: Diagrammatic section of distal end of Kidstonophyton † antheridiophore, from Taylor and Taylor, 1993.
Nothia aphylla †
Nothia aphylla †
Lyon, 1964; Høeg, 1967; El-Saadawy and Lacy, 1979
Early Devonian of Scotland in the Rhynie Chert
Vascular plants with rhizomes and leafless isotomous upright axes
Aerial stems bear lateral and terminal sporangia, and were covered with small emergences, each bearing a stoma
Sporangia were attached by short stalks at the end and along the sides of the stem, in a spiral pattern
Sporangium stalks curved upwards so they were roughly upright
Spores were released through a longitudinal slit that appeared at the apex of the sporangia
Rhizoids present, but no true roots
The gametophyte of this plant was probably Kidstonophyton discoides †
Above: A reconstruction of Nothia aphylla †
Nowenia matsunagae †
Nowenia matsunagae †
El-Abdallah et al., 2026
Plant with smooth axes branching at low angles, branches curved apically close to their base and parallel to subtending axis.
Axis tips circinate.
Branching system comprising two distinct morphologies: densely branched axes, probably upright, and more sparsely branched axes, probably creeping.
K-branching present, subaxillary tubercles or branches absent.
Sporangia solitary, attached laterally on axes, bivalvate, dehiscing along distal and lateral margin.
Spores trilete.
Above: A reconstruction of Nowenia matsunagae †
Odonax borealis †
Odonax borealis †
Early Devonian from Marchin, Belgium
Spiny, mostly isotomous axes, with a spiny branch in a subaxillary position at some proximal branching points
Spines are triangular in outline
The axes end in compact strobili of sporangia
Because of the existence of two dichotomies just below them, the strobili are often borne in groups of four
The strobili are composed of two rows of sporangia, arranged in an opposite to alternate manner
The two rows are borne at 100–150° apart on the same side of the strobilus axis: the strobili thus show a bilateral rather than radial symmetry
Often, the tip of each strobilus is slightly curved
The reniform sporangia are borne erect by a strong spiny stalk bent upwards distally
Dehiscence occurs along their distal margin and opens the sporangia into two equal valves, the abaxial one being spiny
Oricilla †
Oricilla †
Emsian of northern New Brunswick, Canada.
The plant is characterized by apparently erect smooth axes up to 12 cm long and 3–5 mm wide, on which are borne two rows of lateral sporangia.
The sporangia are reniform and attached to axes by a very short stalk oriented perpendicular to the axes
O. bilinearis
Gensel, 1982
O. unilateralis
This taxon has been combined with Amplectosporangium as A. unilaterale
Above: A reconstruction of Oricilla bilinearis † (Gensel, 1982)
Sawdonia †
Sawdonia †
Dawson, 1871
S. acanthotheca
Gensel, Andrews & Forbes, 1975
Emsian of Campbellton Formation of northern New Brunswick
Axes covered with emergences of variable shapes
Probably not a Sawdonia genus (Gensel & Berry, 2016)
S. deblondii
Gerrienne, 1996; Gensel & Berry, 2016
Originally described as Ensivalia deblondii
Early Devonian of Ensival, Belgium
Plant exhibits emergences on axes
Sporangia
Abaxial valve of the laterally-borne sporangia is larger than the adaxial valve
Stalk appears slightly longer and more robust and consistently turns upward so that sporangia are borne in an upright fashion
S. ornata
Dawson, 1871; Hueber, 1971; Gensel & Berry, 2016
Axes up to 4.5 mm wide exclusive of spines, pseudomonopodially branched.
Lateral axes arranged alternately, often to two sides but not always planar, a few possessing an abaxial projection close to the branching point; circinately tipped.
Spines multicellular, tapered, 0.9–3.9 mm long, 0.5–1.8 mm broad at base, tips sometimes darkened, sometimes incomplete, sometimes flared or slightly papillate, density of distribution variable.
Sporangia 1.4–3 mm wide # 1.4–3.4 mm high, stalk 1–1.5 mm wide, 1–1.5 mm long, extending onto abaxial valve; both stalk and abaxial valve with spines 0.2–0.8 mm long.
Epidermal cells isodiametric to elongate, elongation parallel to long axis of plant, cuticular papillae round to oval in outline, centrally located on most epidermal cells; epidermal cell size ranges from 8–20 mm long # 4–6 mm wide; stomata 8 mm wide, 16 mm long, elongation parallel to long axis of stem, margin of pore thickened. Rosettes consist of central often isodiametric cell with thinner, folded cuticle lacking a papilla surrounded by a radiating pattern of elongate papillate cells
S. spinosissima
Schweitzer, 1982
S. wyomingense
Dorf, 1933
Above: Compression fossil of Sawdonia ornata †
Below: Reconstruction of the sporangia of Sawdonia deblondii †
Serrulacaulis †
Serrulacaulis †
Hueber & Banks, 1979
S. furcatus [type]
Hueber & Banks, 1979; Xu, 2011
Frasnian of New Yor State
S. spineus
Xu et al., 2011
Givetian of Xinjiang, China
Above: A reconstruction of Serrulacaulis furcatus †
Tarella trowenii †
Tarella trowenii †
Thrinkophyton formosum †
Thrinkophyton formosum †
Kenrick & Edwards, 1988
Early Devonian (Lochkovian–Pragian) of South Wales
The branching of stems is pseudomonopodial
Left: A reconstruction of Tarella trowenii †
Above, middle: A reconstruction of Thrinkophyton formosum †
Above, right: A compression fossil of Thrinkophyton formosum †
Trichopherophyton teuchansii †
Trichopherophyton teuchansii †
Early Devonian (Pragian) plant from the Rhynie Chert
The aerial axes of the plant exhibit a maximum diameter of 2.5mm
The branching of Trichopherophyton is both dichotomous and pseudomonopodial
It is the only plant known in the Rhynie flora to display circinate vernation.
Generally, the cuticle of Trichopherophyton is poorly preserved, and as a result stomata have not been observed
The rest of the epidermis, however, is usually well preserved and very often exhibits unicellular spinose projections emerging perpendicular to the axis of the plant.
These spiny outgrowths are one of the most characteristic features of Trichopherophyton
The cortex can be divided into a distinct outer cortex comprising closely packed cells and an inner cortex or more loosely packed cells with an inter-cellular air-space network. Many cells of the inner cortex contain dark colored residues
The vascular tissue comprises a very distinct xylem strand. It is sub-terete, exarch and displays both annular and spiral thickening.
A narrow zone, uniform in thickness, of thin-walled cells surrounds the xylem strand and probably represents phloem
Sporangia appear to be reniform (kidney-shaped) with dimensions up to a maximum 3.7 mm by 2.5 mm.
They are attached laterally to the aerial axes with a vascularised sporangial stalk though their spatial distribution is uncertain.
The sporangia appear to be bi-valved with a marginal dehiscence mechanism.
Characteristically the sporangia display the same unicellular spinose projections emerging from the epidermis as seen in the aerial axes
This is the scarcest of the Rhynie plants having only been found in a few beds of chert.
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