Cladoxylalean cladoxylosids

Paracladophyton kespekianum †

• Chu et al., 2024

• Emsian of Quebec, CA

• Paracladophyton appears to be closely aligned with Cladophyton, and is a cladoxylalean cladoxylopsid

• Axes with primary xylem forming multiple long radially oriented ribs, sometimes converging and fusing with adjacent ribs centripetally, and some of the xylem segments converging at the center of the axis. 

• Primary xylem maturation mesarch, with multiple protoxylem strands located along each xylem rib midplane. 

• Lateral appendages with whorled or helical taxis, supplied by single terete centrarch xylem traces that diverge radially from the xylem ribs of the axis. 

• Lateral appendages three-dimensionally dissected, with appendage segments supplied by small centrarch xylem traces.

Polypetalophyton wufengensis †

• Hilton et al., 2003

• Late Devonian of China  

• Branches were produced in an irregular helix, but ultimate appendages were borne in a pinnate arrangement on a frondlike system

• Vegetative "pinnules" were dichotomous and planar (Sphenopteridium-type), whereas fertile "pinnules" were decussately branched and bore fusiform sporangia terminally

• Anatomically, Polypetalophyton is unusual because it has a stele that consists of several primary vascular segments, each of which consists of tracheids and parenchyma surrounded by wood comprising radially aligned tracheids with ray-like slits

  • Similar in anatomy to Cladoxylon taeniatum

• Probably aligned with the Pseudosporochnales. 

  • Polypetalophyton differs from the handful of well-known members of this group in possessing radially aligned xylem and in lacking sclereid nests in the stem cortex. 

• It is also unique in its plagiotropic pinnate frond-like branching system, which we interpret to be the functional equivalent of a leaf or frond. 

• Polypetalophyton represents the first evidence of Sphenopteridium-type foliage occurring within Cladoxylopsids and demonstrates that this kind of foliage has evolved independently within at least three distinct plant clades: zygopterids, cladoxylopsids, and seed plants.

Polyxylon †

• Read & Campbell, 1939

P. elegans 

• Read & Campbell, 1939

• Tournasian of Kentucky & Ohio

P. australe 

• • Chambers & Regan, 1986

  • Late Devonian of Australia

  • Small stem axis with a diameter of 2.7 cm.

  • Anatomy has 19 elongated arms with mesarch primary xylem 

  • Each of the arms branches at the end of dichotomous and forms at least six traces running in the whorled standing side axes.

Rotoxylon dawsonii †

• Cordi & Stein, 2005

• Late Devonian of New York, USA

• The primary xylem consists of 18 radially oriented and elongate primary xylem ribs. 

• Toward the center of the system, some xylem ribs are laterally continuous with adjacent ribs, forming elongate xylem segments, whereas others appear discrete. 

• Order of xylem maturation is mesarch, with one to three protoxylem strands located near the tip of each primary xylem rib.

• Primary phloem immediately surrounds each primary xylem rib and consists of sieve cells. 

• To the outside of the primary phloem, a conspicuous ground tissue is comprised of roughly isodiametric parenchyma with dark contents in their lumina as well as parenchyma cells that are longitudinally elongate with clear lumina. 

• Beyond the vascular column, a fragmentary cortex contains numerous vascular traces embedded in parenchyma. 

  • These latter cells are surrounded by conspicuous masses of longitudinally elongate cortical thick-walled parenchyma. 

• Vascular traces depart from the tips of the primary xylem ribs in a whorled phyllotaxis. 

• Most traces emerge along the midplane of the primary xylem ribs. However, some depart at an oblique angle.