Reinvestigation of the Carboniferous multiovulate cupule Gnetopsis elliptica and its evolutionary significance
Résumé
The genus Gnetopsis was created for dispersed ovules preserved as compressions showing characteristic long apical expansions and for permineralized cupules (Gnetopsis elliptica) containing similar ovules, both from the late Pennsylvanian of central France. Subsequently, several species, on the basis of isolated ovules preserved as compressions of Mississippian to Pennsylvanian age, have been attributed to the same genus. Reexamination of Renault's original material of Gnetopsis shows that the permineralized ovules of G. elliptica have exceptionally well-preserved integument, nucellus, pollen chamber, and megagametophyte with archegonia. Similarity of the ovules of G. elliptica with those of Conostoma is confirmed, but apical expansions are not known in the last genus. Early Permian dispersed ovules, attributed to Gnetopsis (Gnetopsis augustodunensis), also have been reinvestigated; they are very similar to G. elliptica ovules but devoid of apical expansions and are here transferred to the genus Conostoma. Associated organs of stems assigned to the genus Heterangium are believed to have been produced by the same plant. New reconstructions of the ovule and cupule of G. elliptica are presented, along with an emended diagnosis of G. elliptica. The evolutionary significance of this multiovulate cupule is discussed, considering that G. elliptica is more similar in size and organization to some of the earliest (Devonian-Mississippian) cupules than to the contemporaneous Pennsylvanian uniovulate cupules.