Knaus, M. Jane .
The ovulate cupules of Charbeckia macrophylla: new evidence contributing to a whole-plant concept for this possible representative of the Calamopityales.
Recent fossil discoveries of cupulate reproductive structures having attached proximal leaves provide unequivocal evidence for ovulate structures of Charbeckia macrophylla KNAUS ET AL. and possibly the first definitive evidence of reproductive biology for the Calamopityales, an enigmatic Mississippian group known primarily from permineralized stems and petioles. Unlike the typical condition of early seed plants that bore no sterile foliage on their reproductive axes and thereby defy a whole-plant assignment, leaves attached to these cupulate branches display the characteristic outwardly curving dichotomous venation and revolute margins diagnostic of Charbeckia. Argumentation for a calamopityalean affinity was put forth elsewhere based on overall frond size and petiole dimensions. Synapomorphies of the leaf architecture that imply a medullosalean affinity are 1.) venation pattern in two symmetric halves producing a midline, 2.) absence of lobation, 3.) revolute leaf margin, and 4.) off-center notched imparipinnate terminal leaflet. If the Calamopityales-Medullosales did form an early-diverging seed plant lineage (minimum age, Tournaisian) that evolved in parallel with the seed plants leading to conifers, then this new evidence implies that the primitive character state for pre-medullosan seeds was cupulate and further supports the monophylesis of seed plants. Quadripartite cupules are deeply dissected and appear to contain no seeds. Seeds found in close association are exceptionally large and occasionally include the cupule base. In one equivocal specimen, the large seed cupule still bearing the seed with micropylar extensions appears possibly to have been attached directly below the finely dissected cupules. If future discoveries confirm this interpretation, then part of the cupulate system may have assumed a sterile bract-like function leading to the non-cupulate condition of the Medullosales.
1 - Texas State University at San Marcos, Biology, Supple Science Building, San Marcos, Texas, 78666, usa
Presentation Type: Paper
Location: Maybird (Cliff Lodge)
Date: Monday, August 2nd, 2004
Time: 9:30 AM