Anatomically preserved specimens of Cycadeoidea/Bennettites and Williamsonia have provided a wealth of information about a the reproductive biology in a group of Mesozoic seed plants that may be more closely related to flowering plants than is any living clade. Newly discovered seed cones from Upper Cretaceous (Santonian-Campanian) deposits of west coast British Columbia, Canada are permineralized with calcite, and show histological details of the pollen receiving mechanism, megagametophytes and dicotyledonary embryos, as well as new information about post- pollination ovule biology and even pollen tubes. A new species of Cycadeoidea displays spiral contortion of the vascular tissue for several mm below the seed/seed stalk juncture. This tissue is separated from the straight cortical tissues, and does not occur at more proximal levels of the seed stalks. This feature is diagnostic of the contractile roots of living flowering plants, and indicates that some species had cones that retracted their elongated ovules following pollination. Several seeds of one Williamsonia cone show large, branched tubular structures within tissues of the nucellus that are structurally equivalent to the siphonogamous pollen tubes of Agathis australis and other living araucarian conifers. Like the living species, the tubular structures are concentrated in the distal region of the Williamsonia seeds, but some extend to the chalaza. Together with previously documented facets of reproductive ontogeny, these new specimens demonstrate that cycadeoid/bennettite reproductive biology shared numerous derived characters with living conifers, gnetophytes and flowering plants.

Key words: Cretaceous, Cycadeoidales/Bennettitales, Fossil, Pollen Tubes, Pollination Biology