Plant fossils are found coast-to-coast in Canada, from 45-million-year-old mosses in British Columbia to fossil forests on Axel Heiberg and Ellesmere islands in the Canadian Arctic. The early angiosperms developed advantages over contemporary groups — rapid reproductive cycles —  which made them highly efficient, adapting well to "weedy" growth. These modifications, including flowers for the attraction of insect pollinators, proved advantageous in many habitats.

Interaction between plant and pollinator has been a driving force behind the astounding diversification of both flowering plants and insects. Some of the earliest known flowering plants are found in northeastern British Columbia coalfields. Late Cretaceous (about 101–66 million years ago) floras of the Dawson Creek area of British Columbia, and Milk River, Alberta, reveal increasing dominance by angiosperms. These fossils, while generally resembling some living angiosperms, represent old, extinct families, and their relationships to living groups remain unclear.

At the end of the Cretaceous, the climate cooled, inland seas covering much of western Canada drained, and dinosaurs became extinct. At the boundary between the Cretaceous and Paleogene is evidence of extinction amongst land plants, too. During this interval of mass extinction, the Earth was struck by a massive meteorite. The fallout from this impact is preserved in boundary sediments in southern Saskatchewan as a pale clay, rich in rare earth elements such as iridium. 
In the early Paleogene period (66–56 million years ago), we entered the age of mammals. Paralleling the rise of mammals is the rise of modern flora, which consists overwhelmingly of our glorious flowering plants. One of the most prolific fossil sites for Paleogene flowering plants, fruits and seeds is the Messel pit in Germany. In 2012, a research group found over 140 different plant species, 65 of which were previously unknown.

Early Paleogene fossils are found over much of Alberta —  Red Deer River, Lake Wabamun coalfields and Robb to Coal Valley coalfields —  and southern Saskatchewan —  Eastend area to Estevan coalfield —  to as far north as Ellesmere Island. These floras reveal a variety of flowering plants, including members of the sycamore, birch and walnut families, but the most abundant fossil plants are the katsuras and the dawn redwood, now native only to southeastern Asia.