Stauropterid ferns †

Stauropteridales

Members of the Stauropteridales exhibit a relatively ancient morphology for ferns in which there is a poor distinction between stem and leaf tissues. Leaves were not flattened into a single plane and did not produce a blade. This group may represent an evolution of the frond from 3D branching to 2D orientation. Small appendages called aphlebiae occur at each branching point on the plants.

Ecology and Form

    • Small, bushy plants

Stems/Leaves

  • Quadriseriate or biseriate branching

  • Members of this group have relatively ancestral morphology for ferns

  • Poor distinction between stem and leaf tissues

    • Some interpret the branching pattern as the initial stages of the evolution of megaphyllous leaves

  • Leaves did not produce a laminate blade

    • Axes of proto-leaf were not flattened into a single plane.

  • Xylem in cross-section is four-lobed and bilaterally symmetrical

    • Xylem maturation is mesarch

    • No secondary xylem has been found in this group

  • Small appendages, called aphlebiae, occur at each branching point on the plants

Classification

Embryophytes

└Polysporangiophytes

└Tracheophytes

└Eutracheophytes

└Euphyllophytes

└Pteridophyta

└Stauropteridales †

Geologic Age

Diversity

Stauropteris †

S. biseriata (Cichan & Taylor 1982)

  • Early - Middle Pennsylvanian of North America

  • Exhibit distichous branches subtended by a pair of vascularized aphlebiae

  • Taxon exhibits two-ranked branching like modern ferns, unlike quadriseriate branching in other species of Stauropteris

S. oldhamia (Binney 1872)

  • Late Carboniferous

  • Branches born in pairs

  • Six orders of branching have been observed

  • Pairs of highly-dissected aphlebiae exhibited at base of each branch point

S. burntislandica (Bertrand 1909)

  • Early Carboniferous

  • Similar to S. oldhamia, except aphlebiae have greater morphological variation

  • Taxon was heterosporous

    • Megasporangia (Bensonites fusiformis) are spindle-shaped, and the lower half is the distal-tip of the branch

    • There are 2-3 megaspores in the distal portion of the megasporangium, along with possible aborted megaspores

Gillespiea randolphensis †

  • Erwin and Rothwell 1989

  • Devonian (Famennian)

  • Smooth axes with quadriseriate branching exhibiting a protostele that is triangular to 4-sided in large axes, becoming terete in distal axes

  • Heterosporous, but only megasporangia are known

Rowleya trifurcata†

  • Long 1976

  • Pennsylvanian of England

  • Protostelic (tetrarch) axes similar to Stauropteris

  • Laterals branches emerge in 3s; distal axes are terete, in pairs, and interpreted as leaves

Above: Reconstruction of Gillespiea randolphensis (Eggert 1964)

Below: Reconstruction of Stauropteris