Answer:
Pollen and spores (paleopalynology)
Step-by-step explanation:
Fossil pollen and spores are proxy to past vegetation: Paleobotanists use fossil pollen and spores as a proxy to study the extinct plant's species, their complex vegetation patterns, and links to the past climate in the geological time scale. This study is well-recognized as paleopalynology.
Why pollen and spores are preserved as fossils: Both pollen and spores can be preserved and fossilized in the old rocks because they are made up of an extremely resistant organic material known as sporopollenin. Its presence even doesn't allow the complete degradation of the organic material inside in thousands of years.