Sawdoniales †
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
Sporophyte (spore-bearing) phase
Stems
~30cm tall
Pseudomonopodial growth, but distal axes could be isotomously branched
Circinate tips with fiddleheads
Leaves
Leafless
Papillae and spines on stems
Roots
Some members had rooting organs arising from the main aerial axes
These represent some of the oldest known roots in land plants
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
There are gametophytes preserved in the Rhynie Chert that were associated with zosterophylls
Kidstonophyton discoides † was a male gametophyte of zosterophyll, probably Nothia (Remy et al. 1993)
Classification
└Sawdoniales †
Geologic Age
Diversity
Anisophyton †
Remy et al. 1986
Emsian
Bathurstia denticulata †
Hueber 1972; Kotyk & Basinger 2000
Pragian of Bathurst Island, Canadian Arctic Archipelago
Scrambler of about 30 cm in height.
Stems bear short, shelf-like emergences in two rows, and branch isotomously, although sparsely.
Rooting organs, representing some of the oldest known for land plants, arise from the main aerial axes, although they are also associated with small, subordinate shoots interpreted as plantlets.
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: Reconstruction of Bathurstia denticulata showing roots, upright axes, and sporangia (Fig 18, Kotyk & Basinger 2000)
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: compression fossil of Crenaticaulis
Deheubarthia splendens †
Edwards et al. 1989
Axes at least 30 cm tall with spines
Branching is pseudomonopodial and planar, with subaxillary branches
Above: Deheubarthia splendens axis with axillary tubercle branch (Kenrick and Crane, 1997
Above: Reconstruction of Deheubarthia splendens (Kenrick and Crane 1997)
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
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: Forania plegiospinosa reconstruction from Fig 7 of Jensen & Gensel 2013
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)
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 show 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 †
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.)
Oricilla †
Late Early Devonian 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: Reconstruction of Oricilla bilinearis (Gensel 1982)
Nothia aphylla †
Lyon 1964; Høeg 1967; El-Saadawy and Lacy in 1979
Early Devonian of Scotland in the Rhynie Chert
Vascular plant with rhizomes and leafless upright axes bear lateral and terminal sporangia
Aerial stems 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 which appeared at the apex of the sporangia
Rhizoids present, but no true roots
The gametophyte of this plant was probably Kidstonophyton discoides †
Above: Reconstruction of Nothia aphylla
Above: Diagrammatic section of distal end of Kidstonophyton antheridiophore (From Taylor and Taylor, 1993.)
Kidstonophyton discoides †
Early Devonian of Scotland in the Rhynie Chert
Male gametophyte phase of another Rhynie Chert plant, probably Nothia aphylla (Remy et al. 1993)
Sawdonia †
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 †
S. furcatus †
Xu 2011
S. spineus †
Xu et al. 2011
Tarella †
Thrinkophyton formosum †
Kenrick & Edwards 1988
Zosterophyllum †
Z. deciduum †
Lower Devonian (Emsian) of southern Belgium
Plant small in stature
The plant has K and H-branching; some axes are interpreted as rhizomatous
Bifurcation within the fertile region
Another distinctive feature is that the sporangia appear to be deciduous
Often, on fertile axes, only the sporangial stalks remain
The plant is homosporous, the spores being assigned to the dispersed spores species Retusotriletes goensis
Z. divaricatum †
