Dr. Jeffrey M. Osborn
Dean of the School of Science and Professor of Biology
The College of New Jersey
Osborn, J. M., T. N. Taylor, and P. R. Crane. 1991. The ultrastructure of
Sahnia pollen (Pentoxylales). American Journal of Botany 78: 1560-1569.
The micromorphology and fine structure of in situ pentoxylalean pollen are described from the holotype of
laxiphora Drinnan and Chambers 1985 collected from the Lower Cretaceous (Valanginian-Aptian) of Victoria,
southeastern Australia. Pollen grains are ovoid, monosulcate, and relatively small, averaging 26 µm in length.
Exine ornamentation is psilate. The sporoderm is two-parted with the sexine staining lightly throughout and
approximately six times the thickness of the more darkly staining nexine. The exine over the sulcus is
typically strongly invaginated, and may or may not include an extremely thin sexine layer. The outer part
of the sexine is homogenous, while the inner part is composed of relatively large granules separated by
irregular lacunae of various sizes; lacunae are most pronounced at the sexine-nexine interface. Faint
lamellae characterize the nexine in both apertural and nonapertural regions. Granular orbicules are often
associated with the exine surfaces and also occur appressed to pollen sac walls along with lamellated
tapetal membranes. Sporoderm ultrastructure is compared to that of nonsaccate pollen of other groups,
and particularly to pollen of Bennettitales, Gnetales, angiosperms, and similar plants, to which the
Pentoxylales have been thought to be closely related. Although Sahnia laxiphora pollen is not
identical to that of any of these taxa, the strongest similarity is with pollen of Bennettitales.
Anthophyte, Sahnia, Pentoxylales, pollen, ultrastructure, morphology