New information on gametophytes and sporophytes of Aglaophyton major and inferences about possible environmental adaptations

Additional information on gametophytes and sporophytes of Aglaophyton major from the Early Devonian Rhynie chert leads to a much better understanding of many biological and ecological aspects of this early land plant. At least three early ontogenetic stages can be demonstrated, before aerial axes start to develop on the young gametophytes. Only the aerial axes show the essential features of a land plant (stomata, conducting tissue); the initial stages seem more likely adapted to shallow aquatic or edaphic humid than to fully terrestrial environmental conditions. Serial sections of aerial axes of gametophytes and sporophytes of Aglaophyton have yielded new histological and developmental features. These include cuticle structures, stomatal and substomatal features. A hitherto undescribed type of specialized cortical tissue, arrested apices, the formation of second-order axes and bulbil-like organs are documented. New observations on the development of rhizoidal bulges and wound-repair (including conducting) tissues complete this report. The new information provides additional evidence for life (competition) strategies in Aglaophyton, e.g. extensive renewing growth and vegetative propagation. It throws new light upon the adaptive behaviour of Aglaophyton, e.g. protection mechanisms against desiccation of aerial axes. It also illustrates considerable developmental biology of Aglaophyton.