Pseudosporochnales †
Earliest tree-like plants on Earth
The Pseudosporochnaleans were a group of extinct plants that formed some of the first trees on Earth. They were not constructed like modern trees (i.e. copious wood from a cambium); they had many xylem strands in the main axis with small amounts of wood surrounding these bundles. The largest of these plants, Eospermatopteris or the Gilboa trees from New York, was about 8 meters tall exhibiting a large bulbous base with strap-like roots and a long tapering trunk. Attached to the aerial portion of the trunk were leafless branches; the ultimate stem tips were thought to be photosynthetic.
Ecology & Form
Stem
Digitate branching: branch with a series of closely space dichotomies
Many have both primary xylem and secondary xylem
Secondary growth may have been from unifacial cambium; only wood production and not secondary phloem.
Leaves
Leafless with thin photosynthetic stem tips
Reproduction
Produced sporangia in clusters on side branches
Classification
└Pseudosporochnales †
Geologic Age
Diversity
Calamophyton †
Kräusel & Weyland 1929
Middel Devonian
C. primaevum
Originally described from the Middle Devonian of Germany
35 cm long plant reconstructed with finger-like branched main axis
The short, dichotomously branched axes bear a single at each end of the sporangium
In cross-section, stems exhibit a variable number of xylem lobes, ranging from 10 to 33
In the distal parts of the plant, there were fewer xylem lobes
The xylem strands are extended radially in the cross section
Ground tissue of stem exhibits fiber bundles
C. bicephalum
Central axis with finger-like arranged side branches with a diameter of about 1 cm and branch dichotomously
In cross-section, the axis having 14 to 16 xylem segments, which are either oval or have 4-5 radial arms
There are only primary xylem
The "leaves" are three-dimensional structures, each divided dichotomously once horizontally and once vertically
Young leaves in the distal region of the plant bifurcate only once; axes in the lower area divide up to four times
There are indications that leaves and sporangia have been on different axes
The fertile axes are inserted in a pseudowhorl arrangement; sometimes fertile axes are interspersed between sterile whorls
Duisbergia †
Emberger; Taylor et al. 2009)
Characterized by "small, wedged-shaped leaves lacking leaf cushions" (Taylor, Taylor, & Krings 2009)
D. mirabilis
Kräusel & Weyland 1929
Upright, unbranched stem reconstructed to 2 m height, with a club-shaped base
Dense crown of leaves, which are arranged in a tight spiral on the top of the stem
The leaves are arranged in vertical rows
The distal axes consist of fan-shaped leaves (5 cm long)
Well-preserved specimens have up to 60 xylem lobes with secondary xylem arranged in a ring
D. macrociccatricosus
Mustafa 1978; Berry & Fairon-Demeret 1997
Resembles the roots of Pseudosporochnus
This taxon may represent the lower part of the trunk of Pseudosporochnus nodosus (Berry & Fairon-Demeret 1997)
Goldring 1924; Stein et al. 2007
Givetian of Gilboa, NY
Oldest known "tree" on Earth known from the Schoharie Reservior in New York State
Click name for more information
Aerial portions most probably Wattieza (see below)
Hierogramma †
Unger 1856
Small shoot axes
Bilateral vascular system with two elongated xylem strands, one of which is T-shaped.
Distally, the vascular system becomes U-shaped.
Lorophyton †
Fairon-Demaret & Li 1993
Eifelian - early Givetian
Stout trunk with first order branches acutely inserted in a helical fashion
Laterals axes from first-order are branched partly dichotomously.
The distal-most axes are either strap-like or recurved sporangiophores bearing paired sporangia
Pietzschia †
Cross and Hoskins 1951
Late Devonian (Famennian) of Morocco
Similar anatomically to Pseudosporochnus
The stems have a diameter of about 2.5 cm, and have a cylinder of radially arranged xylem plates
P. schulleri (Gothan 1927)
From the Famennian of Morocco,
Primary tissue only; the trunk diameter is often more than 15 cm, the tribe has both central as well as peripheral xylem strands
P. polyupsilon (Read and Campbell ?)
From the New Albany Shale of Kentucky, the number of xylem segments is 54
The main axis had determinate growth; the lateral axes were arranged in whorls
P. timanica (Lepechina 1968)
P. levis (Soria and Meyer-Berthaud 2004)
Lower Famennian (Upper Devonian) of Morocco has aerenchyma indicating that it lived in wetlands
Pseudosporochnus †
Middle-Late Devonian (Frasnian)
Small tree reconstructed with bulbous base
Lateral axes dichotomized several times dichotomous
The terminal branches are three-dimensional
Sterile and fertile units are similar, with the latter possessing paired ellipsoidal sporangia
Sporangia 3 mm long
Pseudosporochnus hueberi has 40-50 xylem strands in main axis and 20-25 in lateral axes
Above: vegetative branches of Pseudosporochnus
Rhymokalon trichium †
Scheckler 1975
Upper Devonian (Frasnian) of New York
3 cm thick stem axis
The second and third order lateral axes are in a spiral arrangement.
Cross sections show a primary xylem strand of less than 1.8 cm in diameter
Plates of xylem with parenchyma in-between
The bark consists of elongated parenchyma cells.
Stenoxylon †
Stenoxylon has plenty of secondary and reduced primary xylem.
Stenoxylon ludwigii has vessel segments anastomose to form a complex network of vascular systems.
At the trunk are numerous small petioles in schraubiger arrangement.
Stenoxylon irvingense from the New Albany Shale has on one side of Xylemarms a stronger form secondary xylem than on the other.
The vascular bundles are more circular. In the parenchymatous ground tissue, there are irregular strips of thick-walled fibers.
Stockmans
Middle Devonian (Givetian) of Belgium and Venezuela
Similar to Pseudosporochnus, with whorls of four, several-times bifurcate laterals that are terminally recurved
Sporangia are elongate and ellipsoid
Distal-most axes are three-dimensional.
Above: Reconstruction of branches of Wattieza
Xinicaulis lignescens †
Late Devonian (Frasnian) of NW China: Bulongguoer Reservoir
Branch vascular supplies are made up of several traces originating from several xylem ribs
Trunk expansion is associated with a cylindrical zone of diffuse secondary growth within ground and cortical parenchyma and with production of a large amount of wood containing both rays and growth increments concentrically around individual xylem strands by normal cambia
The xylem system accommodates expansion by tearing of individual strand interconnections during secondary development
This mode of growth seems indeterminate, capable of producing trees of large size and, despite some unique features, invites comparison with secondary development in some living monocots
Above: Xinicaulis reconstruction (left), and cross-section of stump (right)
Additional Resources
Video of Chris Berry, Ph.D. explaining how these plants grew
First Tree Ripped Themselves Apart (In Defense of Plants, Nov 2017)