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)
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
└Pentoxylales †
Geologic Age
Diversity
Pentoxylon †
Taeniopteris †
