XVI International Botanical Congess

Analysis of unexamined early land plant spores/cryptospores from the Cambrian to the Upper Silurian is illuminating specific structural questions. As yet undescribed dyads and tetrads from the Middle Cambrian Bright Angel Shale have coarsely lamellated walls unlike those seen in later land plant spores and cryptospores. Among the earliest reported trilete spores, specimens from the upper Arenig of the Prague Basin (Klabava Fm.) have homogeneous walls that may be thinner on the entire proximal surface, and extremely thin over the trilete mark. Younger (mid-Silurian - Bloomsburg Fm.) trilete spores (Ambitisporites) have homogeneous walls that are thinner over the contact face but thicker over the trilete mark. Dyads (Dyadospora) with polylamellated walls, like those in the basal Silurian of Ohio, have not been found elsewhere.