Pentoxylales †

Order Pentoxylales †

The Pentoxylales are a group of seed plants that lived during the middle to late Mesozoic. They had long narrow leaves, and wood in a characteristic five-wedge pattern (pento-xylon) around the primary xylem. There were probably trees in form. Reproductively, each ovule was surrounded by a cupule, and structures were unisexual. The diversity of characteristics in leaf venation, stomatal patterning, and ovule structure may indicate that they are cousins to the angiosperms.

Ecology & Form

Stems

  • Short- & long-shoot morphology (like Ginkgo)

  • Eustele reminiscent of Medullosa

  • Wood in five or six wedges around mesarch primary xylem strand (Pentoxylon)

Leaves

  • Foliage arises from short shoots, where leaf scars are commonly visible

  • Leaves long, narrow (Taeniopteris)

  • Syndetocheilic stomata

  • Prominent mid-rib

  • Secondary veins arising at right angles and unbranched to the leaf margin

Reproductive Structures

  • Ovules aggregated into cones or strobili

    • Attached to short shoots

    • Unisexual cones (n.b. this feature may make the Pentoxylales too specialized to be ancestor to angiosperms)

    • Ovules almost completely surrounded by cupule

    • Integument has inner sclerenchymized layer and pulpy outer layer

  • Pollen organs born in clusters on short shoots

Classification

└Embryophytes

└Polysporangiophytes

└Tracheophytes

└Euphyllophyte

└Lignophytes

└Spermatophytes

└Pentoxylales †

Geologic Age

Diversity

  • Pentoxylon †

  • Taeniopteris †