Pollen wall of Ephedra foliata

Abstract

The pollen wall of Ephedra foliata was examined by LM, SEM and TEM. The pollen wall consists of three layers: ectexine, foot layer and endexine. The ectexine has a solid tectum underlain by infratectal processes. The infratectal components appear granular in dried grains but there are columellae‐like rods in fresh fixed grains that were not subject to dehydration and the elevation of ridges. The Ephedra foot layer is part of the ectexine and has the same contrast. There is a white line lamellation between the foot layer and outer component of the endexine that is probably a junction plane between units of the foot layer and the endexine. The endexine consists of many cylindrical sheets that extend parallel with the long axis of the pollen grain. These sheets appear interconnected and may be branched or recurved in some sites. In pollen that had been acetolyzed the endexine was stained lighter than the ectexine, the reverse of most fresh grains. This is due to the endexine being porous and the material held in it is easily extracted by washing, acetolysis, etc. In dried and acetolized pollen grains the ridges are elevated and the lamellae of the endexine are generally appressed. While in fresh fixed pollen the ridges are flattened and the endexine shows gaps between the lamellae. The intine is thick in fresh fixed mature pollen but we have seen no indication of areas having an exceptionally thick intine that could be considered apertural.

The microsporangium of Ephedra is surrounded by a peritapetal lamellation, as in angiosperms. This lamellation extends between tapetal cells as “tapetal (cell) markers.”; The orbicules of Ephedra show a lamellation like those of conifers and angiosperms where such a lemellation results from the formative process. Orbicules of Ephedra are generally large and easily removable from the anthers, therefore they could be favorable objects for study of exine chemistry, function and structure.

There is great variation in pollen morphological characteristics such as size, number and shape of ridges and outline of pollen grains from an individual plant and even within a single microsporangium. This would make it difficult to determine affinities of fossil polyplicate pollen with extant species.