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P ollen morphology and ultrastructure of the B ennettitales : I n situ pollen of C ycadeoidea
Author(s) -
Osborn Jeffrey M.,
Taylor Thomas N.
Publication year - 1995
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1995.tb11573.x
Subject(s) - biology , pollen , ultrastructure , botany , homogeneous , gymnosperm , in situ , morphology (biology) , paleontology , physics , thermodynamics , meteorology
The micromorphology and ultrastructure of in situ pollen from Cycadeoidea dacotensis are described from permineralized specimens collected from the Lower Cretaceous of North America. Pollen grains are ovoid and relatively small, averaging 25 μ m in length and 12 μ m in width. Grains are monosulcate with the exine typically invaginated in apertural regions. Exine ornamentation ranges from punctate to psilate. The exine averages 0.73 μ m in thickness and is composed of a light‐staining sexine and a dark‐staining nexine. The sexine consists of a thin, homogeneous tectum, typically with a well‐defined inner boundary, and a thicker granular infratectum. The infratectal granules are relatively uniform in size, however, variation occurs in the arrangement of granules. In some grains, the sexine appears homogeneous because there is little lacunal space between the individual granules. The granular infratectum is in direct contact with the underlying nexine. The nexine is uniform in thickness in both apertural and nonapertural regions, and it lacks lamellae throughout. Pollen morphology and ultrastructure are compared with those of the bennettitalean genus Leguminanthus and the dispersed genus Monosulcites. In addition, the fine structure of Cycadeoidea pollen is compared to that of the gymnosperm groups with which the Bennettitales are regarded to be most closely related, including Gnetales, Pentoxylales, and Eucommiidites‐type pollen‐producing plants.