Tracheophytes
First vascular plants (possess special cells for moving water)
Tracheophytes are a clade of plants that possess vascular tissue (i.e. xylem / phloem). This group includes all vascular plants, such as clubmosses, ferns, conifers, and flowering plants, but also ancestral and extinct groups such as the rhyniophytes. These basal tracheophytes had tracheids that had a different wall construction than later more derived groups... but it was still xylem.
Ecology & Form
Plants with vascular tissue (i.e. xylem and phloem)
Basal members of this group have S-type tracheids with spongy thickenings (e.g. Rhyniopsida †)
S-type refers to an Early Devonian form genus called Sennicaulis (see below)
Derived forms, Eutracheophytes, have G-type, C-type, or P-type tracheids with lignin in cell wall
Diversity
Rhyniopsida † - e.g. Rhynia
Eutracheophyta - true vascular plants
Above: (right) P-type; (middle) G-type; (left) S-type
Incertae sedis
Bitelaria dubjanski †
Early Devonian from New Brunswick, Canada; Middle Devonian outcrops in the Voronezh region of Russia.
Characterized by thick-walled, dichotomously branched tubular axes and thick cuticles with possible lenticel-like eruptions
Above: Reconstruction of Bitelaria
Bowerophylloides mendozaensis †
Lower Devonian in the Mendoza Province, the Argentine Precordillera
Sterile axes with vertically elongate, fusiform surface features and terminal sessile sporangia borne in pairs
Above: Bowerophylloides mendozaensis † (Plate I, Edwards et al. 2001)
Eohostimella heathana †
Early Silurian (Llandovery)
Possible vascular plant; compression fossils
Branched dichotomously; may have exhibited small spines
Chemistry of fossils similar to vascular plants, rather than algae
Anatomy constitutes upright, cylindrical tubes with a thickened outer cortex, which may have contained traces of lignin or a similar compound,
No tracheids or phloem have been found;
Above: Eohostimella fossils (from Fig.2 Schopf 1966)
Hsüa †
Early Devonian of the Xujiachong Formation, Yunnan, China
Robust main axes (n) 7.0–(10.0)-13.0 mm in diameter, at least 12.8 cm long, creeping and dichotomous. Towards the apex they become upright. Primary xylem centrarch.
Lateral branching systems erect, up to 10.0 cm long; "n" axis bears opposite or alternate laterals
(n+1) at intervals of 3.0–(16.0)-32.0 mm the latter mostly inserted at right angles to the former.
In these examples, many n+1 axes are parallel to the substrate and then turn up.
Towards apex of n axis, n+1 axes are attached at smaller angles.
Fertile n+1 axis dichotomizes equally 1–3 times in three dimensions and produces up to eight distal axes (n+4).
Apices of a pair of distal axes curve in opposite directions and each terminates in a sporangium.
Lateral axes decrease in diameter and length acropetally. n+1 axes are 1/4–1/3 of the width of n axis.
Sparse and irregular minute spines clearly visible on lateral axes but indistinct on main one
Terminal sporangia rounded to reniform in outline
Sporangium dehisces into two equal valves along an indistinct convex marginal thickening.
Spores laevigate with subtriangular amb. Trilete ray 1/2 of the radius.
H. robusta † (Li 1982)
H. deflexa † (Wang et al. 2003)
Above: Hsüa deflexa † reconstruction (Fig 52 from Wang et al. 2003)
Below: Hsüa robusta † reconstruction (Fig 2 from Li 1982
Isidrophyton iniguezii
Plant length is ~30 cm with at 4 dichotomies (isotomous) between 20 and 35 degrees
Axis diameter is 1.3 mm at base, increasing to 0.75 mm
Longitudinal ridges form irregular elongate lenticular structures
Sporangia were ellipsoidal
Above: Isidrophyton iniguezii (Plate II, Edwards et al. 2001)
Jiangyounia gengi
Lower Devonian
Pseudomonopdial stems, smooth
Sporangia are tangentially extended, oval, terminal sporangia
Margophyton goldschmidtii †
Zakharova 1981
Lower Devonian
Originally Psilophyton goldschmidtii but now thought to be a possible zosterophyll with apices and attached root-like structures
Pinnatiramosus qianensis †
Plant with a complex, extensive, pinnate branching system and pitted tracheids from marine Llandovery (lower Silurian) rocks in Guizhou Province, challenges long-held theories on the origin and early evolution of vascular plants in the Silurian and Devonian periods.
This has led to the hypothesis that the fossils are not syngenetic with the entombing rock but represent the rooting systems of much younger plants, possibly of Permian age. Permian strata overly the Llandovery rocks unconformably in the succession.
Leafless axes with less ordered branching occur closer to the boundary and may have had a similar source. Existing and new material of Pinnatiramosus has been subjected to detailed analyses in an attempt to resolve the problem. This has involved examination of the branching systems with respect to the surrounding matrix, comparative morphological descriptions of the systems, and anatomical investigations based on compression and permineralized fossils. The latter in particular indicate an endogenous origin of the lateral branches, typical of roots.
Collectively such evidence is highly suggestive of roots of younger plants growing through lithified sediments—plants whose affinity and age remain to be determined but which show an amazing capacity to fill two-dimensional space efficiently, accompanied by an avoidance strategy that is also seen in recent angiosperms
Polycladophyton gracilis
Lower Devonian
Sporangia are oval and vertically extended
Sporangia terminate short stems in a profusely isotomously branched distal zone
Sennicaulis hippocrepiformis †
Edwards 1981
Early Devonian of Wales
S. hippocrepiformis (Kenrick et al. 1991)
Form genus for sterile axes, circular in cross-section. Xylem exhibits helical thickenings. Tracheid wall is 2-layered: a thin continuous microporiate layer covers a layer with spongy texture
The concept of "S-type" tracheids is named after this plant (image at right)
Above: The S-type tracheids of Sennicaulis hippocrepiformis † (Fig 3, Kenrick et al. 1991)
Taeniocrada
White 1902
Compression fossils of plants with flattened stems which divide isotomously. Stems have prominent midribs; possibly with vascular tissue
This taxon is probably polyphyletic
T. decheniana (Goep.,Kräusel & Weyland 1930)
T. dubia (Kräusel & Weyland 1930)
T. elschanica (Chirkova-Zalesskaja 1957)
T. gracilis (Chirkova-Zalesskaja 1957)
T. latissima (Senkevitsch 1978)
T. lesquereuxii (White 1902)
T. orientalis (Radchenko 1962)
T. pilosa (Senkevitsch 1978)
T. (?) spitsbergensis (Høeg 1942)
T stilesvillensis (Taylor 1986)
Axes isotomous to pseudomonopodial and up to 3.4 mm in width
Distance between branching lessens distally
Axes diverge from 20-75 degrees
Margins are linear often with longitudinal ridges or hair-like projections
T. timanica (Chirkova-Zalesskaja 1957)
T. tuviensis
Above: T. stilesvillensis (Plate I, Taylor 1986)