In the late 1800's when many Cretaceous plant fossils were first being described, paleobotanists named species based on observations of overall similarity. This fossil foliage, for example, which looks similar to that of modern sequoia (Sequoia sempervirens, the coast redwood of California), was named as a new species in the same genus, Sequoia ambigua.
Today paleobotanists are more cautious when they name fossil plants. They know that distantly related plants can look generally similar, and that even the best fossils preserve only some of the features that botanists consider when naming and classifying living species. If the Sequoia ambigua fossils were being described for the first time today, they probably would not be placed in the genus Sequoia, either because of small differences between the fossils and living Sequoia, or out of caution that the few features visible in the fossils don't provide enough information to place them in Sequoia.
As of this writing (2011), no one has published a scientific paper renaming these fossils, so Sequoia ambigua remains the correct scientific name. We have put quotation marks around the generic name, "Sequoia" to indicate we are skeptical that these fossils really belong in the living genus for redwood.