Ancestral euphyllophytes †
"Trimerophytes" etc.
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Early leafless plants with three-dimensional branching
Early leafless plants with three-dimensional branching
Ancestral euphyllophytes, some of which were referred to as "trimerophytes," are an extinct (paraphyletic) group of mostly leafless plants that lived during the latest Silurian-Devonian Period. Trimerophytes get their name from the three-lobed shape of the xylem in stem cross-section, and the trichotomies of branching in some. A lobed stele is considered more complex compared to the cylindrical shape of the rhyniophytes and cooksonioids, allowing for greater surface area to conduct water to lateral organs such as branches and leaves. Additionally, these plants exhibited a pseudomonopodial branching pattern, characterized by upright growth and the development of pseudomonopodial branching pattern, providing upright growth, accompanied by lateral branches. The specialization of branches allowed for structures that could be relegated to support, photosynthesis, or reproduction, which was specialized for the early Devonian. This group of ancestral euphyllophytes gave rise to the cladoxylopsids, the horsetails, the ferns, as well as the progymnosperms & woody plants, making them the ancestors of most living plants.
Ecology & Form
Ecology & Form
Stems
Stems
Morphology
Anisotomous branching in proximal portions
Isotomous branching in distal axes
Anatomy
Actinostele pattern
Centrarch xylem development
Leaves
Leaves
No leaves (?)
See Eophyllophyton bellum † (below) from China, which exhibits rudimentary megaphyllous leaves associated with sporangia
Enations in some
Roots
Roots
Adventitious roots arising from a rhizome is assumed
Reproductive structures
Reproductive structures
Sporangia on bifurcating distal tips after many branching events
Some fertile tips are recurved, pointing back at the main stem
Right: Proposed relationships between early euphyllophytes ("trimerophytes"), Stenokoleales, and Aneurophytales (From Fig. 5, Toledo et al. 2021)
Geologic Age
Geologic Age
Silurian (Ludlow) - Late Devonian
Hostinella may be the earliest record (Kotyk et al., 2002)
Psilophyton clearly established by the Pragian
Classification
Classification
└Euphyllophytes
└"Trimerophytes" †
Most basal taxa of the euphyllophyte clade
Trimerophytes are probably not monophyletic, and represent an ancient grade of early euphyllophyte plants
Diversity
Diversity
Armoricaphyton chateaupannense †
Armoricaphyton chateaupannense †
late Pragian-early Emsian of the Chalonnes Formation in western France
Small, leafless, longitudinally-ribbed axes that branch pseudomonopodially.
Pairs of fusiform-shaped, twisted sporangia preserved as adpressions were found in association with the axes and may belong to this species.
Permineralized specimens reveal the oldest documented wood (secondary xylem) of any known fossil plant.
The water-conducting tissues or tracheids consisted of extinct P-type cell walls.
This type of cell wall consisted of scalariform bordered pits and perforated sheets that covered the openings (apertures) of the pits.
This plant is anatomically similar in some respects to other euphyllophytes, such as Psilophyton and Franhueberia.
Above: 3D and 2D specimens of Armoricaphyton chateaupannense † showing xylem with secondary growth (from Strullu-Derrien et al. 2014)
Chaleuria cirrosa †
Chaleuria cirrosa †
Main axis bearing closely spiraled, monopodial lateral axes, which in turn bear spirally-arranged dichotomous ultimate axes
Pairs of sporangia terminate some ultimate axes
Sporangia bear spores of two sizes, which also differ from one another in shape and ornamentation.
Sporangia contained predominantly large, or predominantly small spores, or a mixture of both
This plant is evidence of euphyllophyte heterospory in the Early Devonian (Emsian)
Above: Chaleuria cirrosa †; a compression specimen (left) and reconstructions (center & right)
Dopyeria elongata †
Dopyeria elongata †
Emsian of Canada
Ribbed axes, less than 1 cm wide; the wider axes dividing slightly anisotomously to produce lateral axes, which divide isotomously up to two times.
Axis anatomy shows a differentially thick-thin layered outer cortex composed of thick-walled cells.
Primary xylem an elongate centrarch haplostele, with or without surrounding secondary xylem.
An elongate lateral trace departs from either end of the haplostele, smaller than parent trace; one end enlarges, and trace divides again to produce two elongate/oval traces.
Secondary xylemconsists of aligned cells with multiplicative division and the presence of spaces, suggesting rays.
Metaxylem and secondary xylem tracheids with tapered ends, scalariform bordered with one or two rows of pitlets.
Distinctive features include the less than 1-cm-wide ribbed axes showing an elongate centrarch haplostele, formation of elongate lateral traces during branching, presence of secondary xylem in larger axes, and scalariform-bordered pitting with multiperforated apertures on tracheid walls.
Douaphyton levigata †
Douaphyton levigata †
Middle Devonian sediments of Xinjiang China
Three orders of axis branching; each axis being less than 2 mm wide
The second-order axes are short, laterally and alternately attached to the main axis.
The third-order axes are paired and anisotomously divided, bearing the vegetative appendages or the fertile units.
The fertile unit consists of a short recurved axis giving off up to four short pedicels along one side, each of which bears one to four pairs of terminal sporangia
Above, left & center: Vegetative specimen and drawing of Douaphyton levigata †; Above, right: Fertile specimen of Douaphyton levigata † (Xu et al., 2017)
Hao & Beck, 1993; Hao et al., 2003
Early Devonian (Pragian), Posongchong Formation of Yunnan, China
Plant represents the earliest record of megaphyllous leaves
Above: A reconstruction of the shoot of Eophyllophyton bellum † (left), and cross sections of the anatomy
Franhueberia gerriennei †
Franhueberia gerriennei †
Early Devonian (Emsian) sediments in the Battery Point Formation of the Gaspe Bay
Basal euphyllophyte with a centrarch protostele and metaxylem tracheids with circular and oval to scalariform bordered multiaperturate pits (P-type tracheids).
The outer layers of xylem, consisting of larger-diameter P-type tracheids, exhibit the features diagnostic of secondary xylem:
Radial files of tracheids
Multiplicative divisions
Combination of axial and radial components
Predate the evolution of stem-leaf-root organography and indicate that underlying mechanisms for secondary growth became part of the euphyllophyte developmental toolkit very early in the euphyllophyte evolution
Above: Anatomy of Franhueberia †, one of the earliest plants to show secondary growth. Cross-section (left) and longitudinal (right)
Gmujij tetraxylopteroides †
Gmujij tetraxylopteroides †
Early Devonian (Emsian) from Battery Point Formation of Quebec, Canada
Small axes with four-lobed primary xylem and secondary xylem.
Primary xylem maturation mesarch, with several shallow protoxylem strands along midplanes of xylem lobes and one central protoxylem strand.
Primary and secondary xylem tracheids with Psilophyton-type secondary wall thickening.
Multiplicative divisions and rays present in secondary xylem.
Mesarch actinostele with Psilophyton-type (P-type) tracheid wall thickening,
Gmujij differs from other Early Devonian euphyllophytes with a new type of anatomical organization in wood production
Comparisons indicate similarity between Gmujij and aneurophytalean progymnosperms, such as Tetraxylopteris.
Its plesiomorphic P-type tracheids set this plant apart from younger actinostelic euphyllophytes
Above: Stem anatomy of Gmujij tetraxylopteroides † (From Fig. 1, Pfeiler & Tomescu 2020)
Hostinella †
Hostinella †
Barrande, 1882
Upper Silurian (Ludlow) of Bathurst Island, Canada, and Early Devonian Senni beds
Dichotomously branching stems (axes); stems are approximately 1.2 mm in diameter
Axes have a striated external appearance
Axes contain xylem with tracheids, 40 µm in diameter.
No known sporangia
It is known to co-occur with the barinophyte, Krithodeophyton
H. bohemica
Kräusel & Weyland, 1932
H. crispa
Arnold, 1939
H. globosa
Lang, 1925
H. heardii
H. hercynica
Mägdefrau, 1938
H. hostinensis
Barrande, 1882
H. racemosa
Lang, 1925
H. racheneuri
Ledoux-Marcelle, 1927
H. silurica
Banks, 1974
H. strictissima
Høeg, 1942
H. wahnbachensis
Kräusel & Weyland, 1935
Above: A-C) Hostinella †; D) Psilophytites † (From Fig. 4, Milagres et al, 2018)
Jowingera triloba †
Jowingera triloba †
Emsian of Battery Point Formation, Gaspé Peninsula, Quebec, Canada
Small axes (~1 mm diameter), roughly circular in cross section
Primary xylem is a three-ribbed actinostele, with ribs extending from the stele center
Conspicuous mesarch protoxylem strands present at the stele center and close to rib tips
This anatomy shows the transition from centrarch to mesarch anatomy and the advent of the condition seen in the monilophytes
Metaxylem tracheids with Psilophyton-type secondary wall thickenings
Phloem forms thin layers in the embayments between xylem ribs and along sides of xylem ribs.
Cortex is a mixture of parenchyma and sclerenchyma; areas of larger-celled parenchyma present outside of the phloem, between the xylem ribs.
Right: Cross-section anatomy of Jowingera triloba †
Kunia venusta †
Kunia venusta †
Late Middle Devonian (Givetian) Haikou Formation near Kunming City, Yunnan Province, China
This plant has three orders of naked axes that divide pseudomonopodially
The second-and third-order axes occur in a helix
Fertile appendages are distantly spaced and helically inserted to the third-order axis
They comprise equally dichotomous branches terminated by two clusters of paired and fusiform (spindle-shaped) sporangia
Sterile appendages are dichotomous and distally recurved
Above: A drawing (left) of the compression fossil (right) of Kunia † from Xiong et al. 2012
Leptocentroxyla tetrarcha †
Leptocentroxyla tetrarcha †
Bickner & Tomescu, 2019 emend.; Tomescu & McQueen, 2022
Emsian of Battery Point Formation, Gaspé Peninsula, Quebec, Canada
Small axes (~2 mm diameter) circular-subcircular in cross-section, with offset opposite decussate pseudo-whorled branching.
Architecture is probably iterative (sensu Berry and Stein, 2000).
Inconspicuous mesarch, shallow protoxylem strands at rib tips.
Primary xylem ~1.1 mm across, a four-ribbed actinostele, with thick diamond-shaped central area and slender ribs.
These central tracheids potentially represent products of an altered protoxylem developmental pathway.
Delayed differentiation and shortened secondary-wall development in the central protoxylem lineage could progressively convert central tracheids into weakly thickened cells and, ultimately, parenchymatous pith.
Leptocentroxyla may be anatomically intermediate between simple basal euphyllophyte steles and more complex Middle Devonian actinosteles
Metaxylem tracheids up to 60 μm wide, with angular, polygonal outlines and Psilophyton-type secondary wall thickenings, except for the conspicuous central area of thinner-walled tracheids with scalariform thickenings derived from simplified Psilophyton-type thickenings
Xylem traces to lateral appendages radially elongated, lacking protoxylem, with central area occupied by a well-defined core of thinner-walled tracheids derived from simplified Psilophyton-type thickenings
Inner cortex wide, parenchymatous, with groups of large sclerenchyma forming a discontinuous layer around the xylem
Outer cortex thin, primarily sclerenchymatous
Epidermis of radially flattened parenchyma
Nebuloxyla mikmaqiana †
Nebuloxyla mikmaqiana †
Emsian (~400 Ma) from Quebec (Canada)
Plant with thin axes with protosteles
Central xylem strand with tracheids displaying Psilophyton-type wall thickenings
Xylem consists of mixed tracheids of variable size and lacks a distinguishable pattern of maturation
Protoxylem is absent or randomly distributed within the xylem
Cortex differentiated into an inner parenchymatous layer and an outer sclerenchyma layer
Plant capable of periderm-type wound response
Oocampsa catheta †
Oocampsa catheta †
Andrews et al., 1975
Eifelian (Middle Devonian) of New Brunswick
Central axis with spirally arranged first-and second-order branches
Second-order branches dichotomize somewhat irregularly to produce ultimate fertile branchlets, located at varied distances along the second-order axes, so that the terminal, erect sporangia occur over a linear distance rather than in dense terminal clusters.
The sporangia are ovoid with pointed apices and contain spores that are trilete, zonate, and ornamented with cones and spines
Above: A compression specimen (left) and a reconstruction (right) of Oocampsa catheta † (from Andrews et al. 1975)
Pauthecophyton gracile †
Pauthecophyton gracile †
Lower Devonian (Pragian) Posongchong Formation near Zhichang Village of Wenshan District, southeastern Yunnan, China.
This plant consists of pseudomonopodially and dichotomously branched main axes and lateral branches.
Some laterals are pseudomonopodially divided producing three to four times dichotomously branched systems terminating in sporangia; other branches are isotomously divided six to eight times terminating in sporangia.
Fusiform sporangia are grouped as fertile units; each unit, generally with two, three or four sporangia, is subtended by a branch which generally divides once or twice.
Sporangia lacking twisting have a longitudinal dehiscence and contain similarly sized spores with laevigate and folded exine.
Pauthecophyton probably occupies a basal position within the euphyllophytes, as one of the earliest divergent clades.
It is more similar to the genus Psilophyton than to others in branching, as well as sporangial shape, terminal position and longitudinal dehiscence
Pauthecophyton and Psilophyton are interpreted as "leafless", but have distal axes with lateral, three-dimensional, synchronously dichotomous trusses that have been called “incipient fronds”, “pinnules”, “dichotomous pinnule-like appendages”, and “proto-leaves” (Kenrick & Crane 1997; Beerling & Fleming 2007)
These were referred to as Branch-Leaf Complexes (BLC) by Hao & Xue (2013)
Above: A compression specimen (left) and line drawings (right) Pauthecophyton gracile †
Perplexa praestigians †
Perplexa praestigians †
Mid-to-late Emsian, South shore of Gaspe Bay, Quebec, Canada
Axes with protostelic primary xylem, with or without surrounding layer of secondary xylem
Primary xylem terete, mesarch, with variable number of protoxylem strands distributed equidistantly close to the periphery of the metaxylem and decreasing in number distally
Metaxylem tracheids with scalariform thickenings, bordered pits and Psilophyton-type thickenings
Secondary xylem with multiplicative divisions and a radial component consisting of radially expanded tracheids and radially curved tracheid ends
Secondary xylem tracheids with Psilophyton-type thickenings
Inner cortex parenchymatous; outer cortex robust, sclerenchymatous, with gaps representing substomatal chambers
Emsian-Eifelian of the USA and Canada
Above: Compression fossils and reconstructions of Pertica quadrifaria †
Planatophyton hujiersitense †
Planatophyton hujiersitense †
Emsian or Middle Devonian locality from the Hujiersite Formation in the Hujiersite area, Hoboksar County, North Xinjiang, North-West China
The plant is possibly rhizomatous and comprises main axes with alternately inserted lateral branching systems
All axis orders bear large triangular enations all over their surface
Lateral branching systems are up to six times dichotomous
Dichotomies in lateral branching systems occur in the same plane, which results in bilaterally symmetrical, two-dimensionally branched organs, with limited overlapping between any segments
Distal segments in sterile lateral branching systems look slightly flattened and/or webbed
The ultimate segments of fertile lateral branching systems bear Psilophyton-like pairs of pendulous twisted sporangia
Anatomy and spores of the plant are unknown
Above: Reconstruction of Planatophyton hujiersitense †
Pleurorhizoxylon yixingense †
Pleurorhizoxylon yixingense †
Three-lobed protostele with mesarch primary xylem, and single protoxylem lacuna in each rib
Thick aligned metaxylem with rays, appearing like secondary xylem, but no cambium or secondary phloem found
Adventitious roots found opposite each primary xylem rib
This is the oldest non-cladoxylopsid to exhibit adventitious root growth
Above: Cross section of the stem anatomy of Pleurorhizoxylon yixingense † (From Fig. 2, Zhang et al. 2018)
Polythecophyton demissum †
Polythecophyton demissum †
Pragian age; the Posongchong Formation of southeastern Yunnan, China
Major axes divide anisotomously to produce irregularly to helically arranged lateral branches
Lateral branches dichotomize once, producing a pair of curved axes; each may dichotomize again, and then produce a series of short, pendulous, lateral fertile systems via unequal bifurcations
Each fertile system may initially bifurcate, and then each component bears 3–4 alternately arranged, short axes terminated by numerous slender fusiform sporangia borne in pairs or in groups of three or four
Collectively, the fertile system is umbrella-like in outline and sometimes bilaterally symmetrical, with a convex upper contour and nearly even lower margin because all sporangia terminate at almost the same level
In some characteristics, i.e., shape of the fertile system, type and attachment of sporangia, it shows similarities with Hedeia, but it differs in its more complex, mostly pinnate distal branching pattern and its pendulous form
Similar in some aspects of branching, sporangial morphology, and sporangial attachment to aneurophytalean progymnosperms
Above: A compression fossil of the fertile portion of Polythecophyton †
Below: A line drawing of the fertile portion of Polythecophyton †
Psilophyton †
Psilophyton †
Dawson, 1859; emend. Hueber & Banks, 1967
Ps. bellum
Dou et al., 1983
May not be a valid taxon
Ps. charientos
Gensel, 1979
Ps. coniculum
Trant & Gensel 1985
Ps. crenulatum
Doran, 1980
Ps. dapsile
This species may represent one of the more ancestral members of this genus
Ps. dawsonii
Banks et al., 1975
late Emsian (Early Devonian)
This species exhibits more complexity in branching than other Psilophyton species
Ps. diakanthon
Fibers form discontinuous layer in inner cortex and two distinct types of spinescent emergences may be anti-herbivore defense.
Ps. forbesii
Andrews et al., 1968
Pseudomonopodial main axis
Spiral-arrangement of laterals
Ps. genseliae
Gerienne, 1997
Ps. goldschmidtii
Dou et al., 1983
Ps. krauselii
Obrhel, 1959
Ps. microspinosum
Kasper et al., 1974
Ps. parvulum
Gerienne, 1995
Ps. primitivum
Hao & Gensel, 1998
Ps. princeps
Hueber & Banks, 1967
Ps. szaferi
Zdebska, 1986
Above, left: stem xs showing 3-lobed xylem; Above, right: Reconstructions of Psilophyton †.
Below: Psilophyton diakanthon † three-dimensional reconstruction of axis and spines as seen from five different angles. Asterisks mark the tips of spines of two distinct morphological types: shorter, sturdier, barb-shaped spines with short-tapering apically curved tips (white asterisks) and longer, straighter spines that diverge obliquely upwards from the axis at relatively sharp angles (orange asterisks); arrowheads mark ‘dimples’ in the axis surface interpreted as marking the locations of sunken stomata. Scale bar = 1.5 mm (Colston et al. 2022)
Shougangia bella †
Shougangia bella †
Late Devonian (Famennian), Wutong Formation of Anhui and Jiangsu Provinces, South China
Fern-like euphyllophyte that evolved tone of the earliest known laminate structures (leaves?)
Stems contain a dissected stele with a four-ribbed and an elongate curved primary xylem segments changing to three elongate and slightly curved segments.
Primary branches have a dissected stele with three similar primary xylem segments as in stems.
The primary xylem of the stems and primary branches is mesarch, and individual primary xylem segments bear peripheral protoxylem strands and are surrounded by secondary xylem.
Stenoloboxyla ambigua †
Stenoloboxyla ambigua †
Emsian of Gaspé (Quebec, Canada)
Small axes (~2 mm diameter)
Primary xylem bar-shaped to trilobed in cross section
one of the lobes shallow, sometimes barely protruding
Inconspicuous mesarch protoxylem strands at rib tips, central protoxylem strand absent
Psilophyton-type secondary wall thickenings
Inner cortex wide, parenchymatous, with groups of large, thick-walled sclerenchyma forming a discontinuous layer around the xylem
Outer cortex thin, consisting primarily of thin-walled sclerenchyma with some interspersed parenchyma
Epidermis with ± isodiametric parenchyma
Right: Cross-section of the stem anatomy of Stenoloboxyla ambigua †.
Tainioxyla quebecana †
Tainioxyla quebecana †
Emsian of Gaspé (Quebec, Canada)
Hypothesized to exhibit early stages of vascular cambial growth (brackets in image)
Axis fragments about 1.8 mm and 2.3 mm in maximum width.
In cross sections, the central primary xylem is a mesarch protostele that forms an elongated shape (1.3 × 0.6 mm).
At least four protoxylem strands are located along the midplane of the stele and close to the two ends
A sharp change in tracheid diameter characterizes the transition from protoxylem to metaxylem.
Metaxylem tracheids are isodiametric to slightly elongated in a direction perpendicular to the long axis of the protostele, and exhibit markedly angular outlines and widely variable diameter, up to 108 μm.
Tracheid size generally increases away from the protoxylem strands, but smaller tracheids are present at places around the periphery of the xylem.
The tracheids display P-type pitting.
Adjacent to these cells are narrower, thin-walled cells (17–24 μm; mean = 21 μm; n = 4), often incompletely preserved, that probably represent phloem
The inner cortex, incompletely preserved, has variable thickness ranging from c. 100 μm in one of the axes to 400 μm in the other (Fig. 16, 18).
The transition between the parenchymatous inner cortex and the primarily sclerenchymatous outer cortex is sharp.
Stomata are present in the epidermis (Fig. 24, 25) and the bell-shaped sub-stomatal chambers underneath them lend the sclerenchymatous outer cortex a discontinuous appearance
Right: Cross-section of the stem anatomy of Tainioxyla quebecana †.
Tenuisa frasniana †
Tenuisa frasniana †
Late Devonian (Frasnian) from Hunan Province of South China
Axes are naked and narrow
Reproductive:
Fertile stem is pseudomonopodial in branching and bears distichous laterals
Fertile laterals are subopposite and pseudomonopodial in the proximal part of the stem
They become alternate and isotomous two to four times in the distal part.
Fertile laterals have tiny terminal sporangia that are paired and fusiform and that possess pedicels.
Vegetative:
Sterile ultimate units are dichotomous and terminate in tips recurving oppositely.
Tenuisa resembles Psilophyton in pseudomonopodial fertile stem with alternate and dichotomous lateral units terminated by paired and vertically elongate sporangia.
However, fertile lateral units are subopposite and pseudomonopodial on the basal part of the stem, sporangial pedicels are present, and neither sporangial pairs nor sporangia themselves are twisted.
Above: Compression fossils of Tenuisa frasniana † axes exhibiting fertile unit (Wang, 2007)
Tsaia denticulata †
Tsaia denticulata †
late Middle Devonian (Givetian) of North Xinjiang, China
Type specimen
Plant possesses small axes covered in deltoid spines
Brnaching is predominantly anisotomous
Elongate sporangia with small distal spines are carried terminally in clusters on short branches which have a number of close distal dichotomies
These plants are superficially similar to Psilophyton, but can be distinguished from it by the anisotomous lateral branching systems, by the spiny extensions to the sporangia, and by the details of the sporangial attachments
Above: Compression fossils of Tsaia denticulata †, Plate II, Wang & Berry, 2001
Trimerophyton robustius †
Trimerophyton robustius †
Dawson, 1859; Hopping, 1956
Emsian of Canadia
Originally named Psilophyton robustius
Aerial axes smooth
Main axis branched to form a dichotomy, but secondary branching formed trichotomies, which give the plant the name "trimero-"
Branches were terminated by elongate sporangia
Wilhowia phocarum †
Wilhowia phocarum †
Early Devonian (Emsian) of Gaspe Bay, Canada
Plant with at least three levels of branching; perhaps up to 1 m tall
Main axes branch pseudomonopodial, bearing helically arranged, single or paired, long first-order axes
First-order axes produce helically arranged, cruciately dichotomous ultimate axes, terminating in acuminate, recurved tips or in clusters of paired, fusiform sporangia.
Sporangia in each pair curve or bend around each other near distal tips
All axis orders covered with small, sharply tapered, multicellular emergences.
Main axis a mesarch, three-ribbed actinostele composed of primary xylem with P-type and occasionally circular pitting
Protoxylem present at center and near the tips of each rib, sometimes represented by lacunae and evident as median bands or elongate regions in some ribs
Xylem parenchyma absent.
Trace formation via tangential elongation of rib tip, then separation of an oval trace with central elongate protoxylem.
Cortex two zoned, inner cortex not preserved, outer cortex with irregularly patterned, thin- to moderately thick-walled cells.
Paired first-order branches with cortex of thinner-walled parenchyma cells produce a vascular trace with central protoxylem dividing either before or after its separation from ribs, resulting in two and sometimes three (perhaps four?) oval traces
First-order traces elongate at one end to produce a smaller round-oval second order trace
Epidermis consisting of small, tightly packed, square to rectangular cells
Undoubted stomata not present, but gaps in epidermis/ outer cortex present.
Emergences multicellular, broader at base, and sharply tapered. Cortex composed of parenchyma cells of varying thickness, possible remnants of phloem present.
Above: A reconstruction of Wilhowia phocarum †
Wutubulaka multidichotoma †
Wutubulaka multidichotoma †
Late Silurian (Pridoli) of China
This taxon shows complex branching for a late Silurian plant
Naked axes with first-order pseudomonopodial branching
Fertile units alternately attached to a second-order axis, having a dichotomous branching system with two sporangia at each tip
Sporangia narrowly obovate, with tapering base and round apex
Few characters place this as a euphyllophyte, but similarities to the branching of Psilophyton may indicate this placement
Above: A reconstruction of Wutubulaka multidichotoma †
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