incomplete exine development in aborted pollen of eupatorium serotinum michx. (compositae: eupatorieae)

Mature anthers of Eupatorium serotinum Michx. (Compositae: Eupatorieae) have fully formed pollen grains along with microspores that apparently aborted during several stages in development. The latter are enclosed by acetolysis-resistant sacs. The least developed microspore exine (presumably the youngest stage) consisted of rods about 100 nm in diameter, without spines and mainly without a tectum. A more advanced stage had a discontinuous tectum with many unattached columellae and with cylindrical spines having a flat or slightly convex summit. In the most advanced aborted microspores the tectum was variable but mostly continuous and the spines were greatly increased in diameter and all had rounded distal ends. The special feature of these stages was the gaps in the basal portions of the forming spines. The gaps were open basally and filled with structure of the same appearance as columellae and tectum. These results contribute to direct evidence that microspore exines that had aborted early in their development retain the features in mature anthers of that stage(s) of exine development at the time of their abortion. Providing that the mature anthers also contain mature pollen with fully developed exines (typical of the taxon), then the underdeveloped exines within such anthers can provide information about early development. Underdeveloped exines such as those recovered in intact anthers in sedimentary rocks, may provide information about ontogeny that otherwise would be unobtainable.