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Plants with true water-conducting cells (i.e., xylem)
Plants with true water-conducting cells (i.e., xylem)
Eutracheophytes are the clade of plants with true vascular tissue (i.e. xylem/phloem). This group includes all vascular plants, such as clubmosses, ferns, conifers, and flowering plants, but also (sometimes) an ancestral group called the cooksonioids. Basal eutracheophytes had tracheids that had a different wall construction than modern forms. N.b., this term applies to both xylem and phloem, but because of poor preservation of soft phloem tissues, most fossil taxa are included in this group based upon the secondary wall thickenings of the xylem.
Ecology & Form
Ecology & Form
True vascular plants
Xylem cells with thick, decay-resistant walls
Pitting between thickenings on xylem cells
This group includes all modern vascular plants, as well as C-type, G-type, and P-type xylem cells.
This group excludes S-type xylem, as well as non-vascular & para-vascular plants
Geologic Range
Geologic Range
Silurian - present
Diversity
Diversity
Cooksonioids † - e.g., Cooksonia †
Lycophytes - e.g., zosterophylls †, clubmosses, spike mosses, quillworts
Euphyllophytes - e.g., "ferns" (monilophytes) and seed plants
Incertae sedis
Incertae sedis
Aarabia brevicaulis †
Aarabia brevicaulis †
Early Emsian of Central Morocco
Branching is pseudomonopodial in all orders of axes.
Distinction is made between short and long branches.
Short branches consist of a foreshortened axis dichotomising in two terminal segments recurved abaxially and adaxially towards the axis of previous order. Arrangement of short laterals on main stem is unpredictable.
It is typically proximal on long branches.
Long branches of all orders are characterised by short internodes proximally, that increase in length distally.
Fertile branches display few anisotomous divisions and bear a small number of non-paired elongated sporangia.
Associated large spores in the vicinity of the fertile appendages suggest that the plant might have been heterosporous
Right: reconstruction of Aarabia brevicaulis
Aberlemnia caledonica †
Aberlemnia caledonica †
Edwards, 1970; Gonez & Gerrienne, 2010
Formerly Cooksonia caledonica
Early Devonian
Right: Reconstruction of Aberlemnia caledonica (Figure 7 from Gonez & Gerrienne, 2010)
Adoketophyton †
Adoketophyton †
Early Devonian (Pragian) of Wenshan district, Yunnan, China
Distal aerial parts of the plant with smooth dichotomously branching axes and terminal strobili composed of compound lateral fertile units
Each unit comprises a bract-like flattened appendage and a single adaxially inserted sporangium with two valves and distal dehiscence around a convex margin
This group was thought to be a barinophyte, but it lacks all the features of that group
Even though it appears to be aligned with lycophytes, "...this plant is considered to be independent of the Zosterophyllopsida on the basis of the fertile unit composed of fan-shaped leaves and adaxially attached sporangia, and from Lycopsida in the absence of vegetative microphylls and presence of vegetative terminal circinate tips" (Hao & Xue, 2013)
This plant has centrarch maturation, which differs from the exarch xylem maturation of lycophytes
A. subverticillatum †
Originally named Zosterophyllum subverticillatum
A. parvulum †
Axes naked. Isotomously or pseudomonopodially branching, with vegetative ultimate tips circinately coiled.
Fertile axes naked, dichotomously branching at angles of 25°–55°.
Strobili parallel-sided, comprising four rows of oppositely and decussately inserted fertile units; the longest strobilus with more than 60 fertile units; each fertile unit consisting of a sporophyll and an adaxial sporangium.
Sporophyll fan-shaped, with a short pedicel, and the laminar region partly enclosing the sporangium.
Sporangia elliptical, attached to the adaxial base of the sporophyllous lamina by a short stalk, with distal dehiscence along convex margin.
Height of sporophyll lamina and associated sporangium almost equal, 0.8–1.4 mm.
Anatomy unknown.
A. pingyipuensis †
Vegetative parts unknown
Parallel-side strobili with sporangial complexes inserted on all sides of the strobili
Sporangial complex above junction with stalks
Stalks parallel sided, adxially curved such that complexes are held upright or slightly reflexed
Ovoid sporangia lacking stalks attached near the base of a fan-shaped bract that partially curves around sporangium and extends beyond it
Above: Adoketophyton parvulum † reconstruction (Fig 2, Zhu et al., 2011)
Bracteophyton variatum †
Bracteophyton variatum †
Late Pragian–lower Emsian of Qujing District of eastern Yunnan, China
Smooth axes, mainly isotomous, which terminate in short and compact strobili consisting of lateral fertile units arranged helically.
Each fertile unit comprises one or two bracts and an elongate-ovate adaxial sporangium.
The sporangium seems to possess a distal dehiscence around the convex margin.
This plant differs from bract or sporophyll-bearing plants such as Stachyophyton, Adoketophyton, and the Barinophytes mainly in the shape and variable number of bracts in a fertile unit.
In the absence of vegetative microphylls, it is morphologically far less related to the lycopods.
Resembling the sporangial arrangement in spikes of some zosterophylls, the fertile units form terminal compact strobili that demonstrate developmental changes in the apical meristem.
Right: Bracteophytum variatum fertile shoots
Changwuia schweitzeri †
Changwuia schweitzeri †
Lower Devonian of Guangxi Autonomous Region in China
Central axis from which lateral branching systems are borne helically and at short distances from one another.
Lateral branching systems have a diagnostic morphology which have the initial appearance of either synangia or cupules, and terminate in numerous long and slender lobes.
Changwuia has a comparatively advanced organization for the time period
Right: Changwuia schweitzeri
Danziella artesiana †
Danziella artesiana †
Danzé-Corsin; Edwards, 2006
Early Devonian from Artois, France
Originally named Zosterophyllum artesianum
Smooth axes with lateral stalked sporangia comprising two equal valves
Fertile stalks attached at right angles to the axes, and are long and straight
Distal dehiscence occurs in the same plane of compression as the subtending axis
Sporangia are attached at irregular intervals and there is no well-defined spike
Right: Danziella artesiana
Dibracophyton acrovatum †
Dibracophyton acrovatum †
Lower Devonian (Pragian) Posongchong Formation of Wenshan District, southeastern Yunnan, China.
The plant has creeping axes from which arise vegetative and fertile axes.
The vegetative axes helically bear lateral dichotomous appendages with curved or round tips.
The fertile axes possess terminal strobili with numerous fertile units arranged in irregular helices.
Each fertile unit consists of a stalked long-elliptical sporangium, with dehiscence into two equal valves, and two discrete long-ovate bracts covering sporangium from above–below directions.
It may be closely related to the Barinophytes in affinity.
Right: Reconstruction of Dibracophyton
Stachyophyton yunnanense †
Stachyophyton yunnanense †
Early Devonian of Yunnan, China
This plant shows some similar organization in fertile region and sterile parts in comparison with other Devonian genera (Protolepidodendron, Colpodexylon, Leclercqia, Enigmophyton, Krithodeophyton).
It may be that the plant represents an intermediate stage in evolution between Enigmophyton and Krithodeophyton, and shows perhaps a certain affinity to lycopods.
According to the salient features of Stachyophyton, it can not be, at present, placed in any group known in vascular plants.
It can be assigned to a definite position of taxon basing on much fossils record and further studies
Right: Reconstruction of Stachyophyton
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