Phytoliths are microscopic deposits of silica produced by plants. They form when silicic acid reaches supersaturated concentrations within plant tissues, frequently resulting in taxon-specific morphologies. Phytoliths represent a valuable proxy in paleovegetational, paleoenvironmental, and paleoclimatic studies, where morphological similarities between detrital fossil phytoliths and those of modern plants have been used to infer the identity and presence of ancient plant taxa. However, the degree of morphological stasis between the phytoliths of extant plants and their fossil relatives has yet to be empirically examined. Here, phytoliths are extracted from a phylogenetically broad sample of foliar macrofossils spanning the Cretaceous, Paleocene, and Eocene periods to assess their morphological resemblance to phytoliths from related modern plants. Leaf macrofossils from dicot, palm, and conifer taxa underwent a specialized physiochemical extraction protocol to remove extraneous sedimentary material and isolate potential contained phytoliths. Foliar provenance was confirmed by comparing the abundance of phytoliths within the fossils to that of surrounding sediments. Phytoliths were similarly recovered from leaves of extant taxa affiliated with fossil specimens for morphological comparison. Fossil and modern phytoliths were observed and morphologically described using optical and scanning electron microscopy. Overall morphotypic similarities between the phytoliths of related fossil and modern taxa suggest that fossil taxonomic assignments based on modern morphologies are appropriate in these groups. This study demonstrates that autochthonous phytoliths persist within leaf macrofossils—the paleoecological significance of this observation is discussed. Phytoliths from taxonomically identifiable macrofossils not only demonstrate the deep-time persistence of phytolith form, but also allow for examination of potential evolutionary shifts in phytolith morphology, possible refinement of macrofossil taxonomic assignments, and the taxonomic identification of enigmatic detrital fossil phytoliths.