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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 & 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

└Stauropteridales †

Geologic Age

Devonian - Pennsylvanian

Diversity

Stauropteris †

Binney, 1872
S. americana
- Darrah, 1941
- Pennsylvanian (Moscovian) of Iowa, USA
S. berwickensis
- Long, 1966
- Early Carboniferous of Scotland
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. burntislandica
- Bertrand, 1909
- Early Carboniferous of Scotland
- 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
S. oldhamia

Binney, 1872
Pennsylvanian of UK
Branches are born in pairs
Six orders of branching have been observed
Pairs of highly dissected aphlebiae exhibited at the base of each branch point

Above: Reconstruction of Gillespiea randolphensis (Eggert 1964)

Below: Reconstruction of Stauropteris

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

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