Melanie A. Glees
Project Topic / Abstract:
"Pollen Development in a permineralized Pine from the middle Eocene Princeton Chert (Allenby Formation) of British Columbia, Canada"
The Princeton chert locality in southern British Columbia
represents one of the most well preserved and most diverse
Tertiary assemblages of permineralized plants known, and in
recent years, it has provided abundant information regarding
Middle Eocene angiosperms and many of their fungal
parasites. Additionally, two polypodiaceous ferns and the
conifer genera Metasequoia and Pinus have been described
from the chert. Pine fossils are circumscribed by four
species and are known from leaves, woody twigs, dwarf
shoots, and ovulate cones. Pollen cones found in association
with P. similkameenensis leaves and P. arnoldii ovulate
cones have also recently been described. In addition to a
large number of mature pollen cones, variations in cone
size, cone anatomy, and pollen morphology indicate that
several ontogenetic stages are preserved within the chert.
Pollen cones are ellipsoidal, range from 2.8 to 6.9 mm in
length and 1.6 to 3.5 mm in diameter, and are subtended by
scale leaves. Microsporophylls are helically arranged and
each bears two abaxial pollen sacs, many of which contain
bisaccate pollen grains. Developmentally, cones vary with
respect to the degree that they are surrounded by the
subtending scale leaves, as well as the number and the
morphology of the cell layers composing the pollen sac wall.
Aspects of pollen ontogeny that have been documented include
the following stages: tetrad stage, formation of the
aperture and apertural membrane, formation of sacci, and
formation of the homogeneous nexine and the
tectate-alveolate sexine wall layers. The Princeton chert
specimens represent the oldest pollen cones described for
Pinus and the only fossils of the genus for which pollen
ultrastructure, including ontogenetic characters, has been
described.
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