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

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

  • Leclercq and Andrews 1960

  • Middle Devonian

  • 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

  • Middle Devonian

  • 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)

Eospermatopteris eriana †

  • 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

  • Givetian

  • 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.

Wattieza †

  • 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

Xenocladia †

  • Arnold 1940

  • Middle (Givetian) to Late Devonian (Frasnian)

  • Liana growth form was proposed.

  • Stems of Xenocladia medullosina have a diameter of about 10 cm and possess secondary xylem.


Xinicaulis lignescens †

  • Xu et al. 2017

  • 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