STOCKEY, RUTH1* and GAR W. ROTHWELL2. 1Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada; 2Department of Environmental and Plant Biology, Ohio University, Athens, Ohio, 45701, USA. - An ovulate Williamsonia cone from the Upper Cretaceous of western North America.
One anatomically preserved ovulate cone similar to those of the
cycadeoidalean/bennettitalean genus Williamsonia has been
recovered from the Upper Cretaceous (Santonian) sediments of Vancouver
Island, British Columbia, Canada. This well preserved and nearly
complete specimen consists of a receptacle that bears tightly packed
interseminal scales and ovulate sporophylls with terminal ovules.
Sporophylls and interseminal scales extend from the receptacle around
an arch of more than 300 degrees. Interseminal scales do not show an
epidermis except at the apex, and the boundaries between adjacent
interseminal scales are not discernible. In cross sections the ovules
are round to elliptical at all levels, and the sarcotesta consists of
small radial projections. There is no cupule. The vascularized
nucellus is attached to the integument only at the chalaza, and it
terminates apically in a cellular projection that fits tightly into
the micropylar canal. No pollen chamber is produced. Several ovules
show highly branched structures that are comparable to the pollen
tubes of living araucarian conifers. Cellular megagametophytes and
immature embryos demonstrate that archegonia are positioned laterally,
in the apical region of the seed cavity. The superb preservation of
these specimens allows for clarification of several systematic
characters, and for the interpretation of pollination biology.
Key words: Bennettitales, Cycadeoidales, Pollen Tubes, Seed Cone, Williamsonia