Dr. Jeffrey M. Osborn

Publication Abstract

Osborn, J. M. and T. N. Taylor. 1994. Comparative ultrastructure of fossil gymnosperm pollen and its phylogenetic implications. In: M. H. Kurmann and J. A. Doyle (Editors), Ultrastructure of Fossil Spores and Pollen , pages 99-121. Royal Botanic Gardens, Kew, UK.

Numerous studies have been carried out on fossil gymnosperm pollen detailing its overall appearance in transmitted light and, to some extent, its surface morphology as revealed by scanning electron microscopy. Fewer investigations, however, have addressed the fine structural nature of fossil pollen using transmission electron microscopy (TEM). Pollen wall ultrastructure from grains preserved within intact reproductive organs (in situ) has been documented from gymnospermous taxa of the following orders: Lyginopteridales, Medullosales, Callistophytales, Cordaitales, Glossopteridales, Voltziales, Coniferales, Caytoniales, Corystospermales, Cycadales, Cycadeoidales, and Pentoxylales. Several dispersed (sporae dispersae) pollen types are also known from a few of these groups as well as the Gnetales. Moreover, a number of other taxonomically enigmatic palynomorphs (both in situ and dispersed taxa) have been described at the ultrastructural level, and are currently classified as incertae sedis. Pollen morphology and ultrastructure of these groups have played an important role in recent phylogenetic studies, which have been based on a number of reproductive and vegetative characters. Although many palynological characters are generally considered conservative features and thus manifestations of phylogeny, they can also reflect several other biological and physical phenomena. For example, features associated with pollen ontogeny as well as pollination syndromes may be important influences, while the most prominent abiotic factors to consider are mode of preservation, degree of diagenesis, and a suite of preparation protocols. These features are discussed as they relate to phylogenetic interpretations and relevance of several salient palynological characters, including overall exine infrastructure, nexine organization, and saccus type and internal composition.

Gymnosperms, In situ pollen, Sporae dispersae pollen, Review, ultrastructure, morphology