Eutracheophytes
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 an ancestral group called the cooksonioids. These 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
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 & pre-vascular plants
Geologic Range
Silurian - present
Diversity
Cooksonioids † - e.g. Cooksonia †
Lycophytes - e.g. zosterophyllophytes †, clubmosses, spike mosses, quillworts
Euphyllophytes - e.g. "ferns", seed plants
Incertae sedis
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 †
Edwards 1970; Gonez & Gerrienne 2010
Formerly Cooksonia caledonica
Early Devonian
Right: Reconstruction of Aberlemnia caledonica (Fig 7 from Gonez & Gerrienne 2010)
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
Changwui 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: Changwui schweitzeri
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 †
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 †
Posongchong Formation (Siegenian) of the Lower Devonian in Wenshan district,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 plant.
It can be assigned to definite position of taxon basing on much fossils record and further studies
Right: Reconstruction of Stachyophyton
