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
└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 †
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†
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
