Mesozoic and Cenozoic plant evolution and biotic change: A symposium in honor of Ruth Stockey
Klymiuk, Ashley A , Stockey, Ruth A , Rothwell, Gar W .
Enclosed seeds from Apple Bay provide insights to Early Cretaceous gymnosperm diversity.
The Apple Bay flora of Vancouver Island, British Columbia (Lower Cretaceous, Valanginian) provides an important window into the composition of terrestrial vegetation immediately before the initial phylogenetic radiation of angiosperms. In addition to fungi, lichens, liverworts, mosses, lycophytes, equisetophytes, and ferns, the assemblage contains pinaceous and cupressaceous conifers, cycadeoids, a gnetophyte, and the enigmatic cupulate seed Doylea tetrahedrasperma. Here, we report a second form of uni-ovulate seed-enclosing structure from the Apple Bay assemblage. Three specimens representing a range of developmental stages have been studied and reconstructed from cellulose acetate serial sections, using AVIZO, Slicer, and Blender software packages. The orthotropous seeds are tetrahedral (at least 4.4 mm long by 2.2 mm wide) with an elongated micropylar canal, and complex integument with zones resembling the sarcotesta, sclerotesta, and endotesta of some Paleozoic ovules. The nucellus separates from the endotesta at the chalaza; the most mature specimens contain cellular tissue within a prominent megaspore membrane. Except at the tip of the micropylar canal, the seed is completely enclosed by an outer cupule-like structure, which shows no evidence of having developed from separate precursors (e.g., from the bracts of some cupressaceous conifers or the bracteoles of gnetophytes). The cupulate structure is 0.5 to 1.0 mm thick, and composed of two zones of thin-walled parenchyma cells. Within the outer zone there are ca. 20 secretory canals with a distinctive epithelial lining. The canals originate separately near the base of the cupulate structure, and extend its length, terminating just below the apex. The cupulate structure is vascularized by a triangular woody stele, composed of a parenchymatous pith surrounded by radially-aligned tracheids with scalariform thickenings. Within the cupulate structure, three short terete traces diverge from the corners of the stele, which terminates as transfusion tissue below the sclerotesta at the base of the seed. These new enclosed seeds share some features with gnetophytes and dispersed gnetophyte-like seeds from Cretaceous sediments of Europe and North America. However, the distinctive vascularization, resin canals of the cupulate structure, nature of the nucellus and integument, and configuration of the micropylar canal distinguish these specimens from previously recognized gymnospermous clades, further expanding the range of gymnospermous diversity at the onset of the Cretaceous.
1 - University Of Kansas, Ecology & Evolutionary Biology, Rm 45Takeru Higuchi Hall, Kansas Biological Survey, 2101 Constant Ave, Lawrence, KS, 66047, USA
2 - Oregon State University, Department Of Biological Sciences, 2082 Cordley Hall, Corvallis, OR, 97331, USA
3 - Oregon State University, Department Of Enviromnental & Plant Biology, 2082 Cordley Hall, Corvallis, OR, 97331, USA
Presentation Type: Colloquium Presentations
Candidate for Awards:None