XVI International Botanical Congess

The Late Devonian progymnosperm tree Archaeopteris freely shed its megaspores and microspores from sporophylls clustered into fertile leaf zones of strobili on some ultimate branches. Reproductive census techniques were used to scrutinize strobilus composition and construction. From exemplar species (A. halliana, A. macilenta, A. obtusa), sporangia were extracted, cleared, and classified based on content. Spore types were mapped according to position (proximal/distal) in the overall strobilus and fertile branch system. Spore distribution was analyzed for intra- and inter-strobilus patterns by ANOVA and regression methods developed for the study of fertile organization in living Selaginella. Conclusions on sporangium arrangement, construction, and overall strobilus architecture, provide new insights on spore dispersal mechanics of an Archaeopteris tree canopy.