sporopollenin

thumb|right|270px|Scanning electron microscope (SEM) image of [[pollen grains]]

Sporopollenin is a biological polymer found as a major component of the tough outer (exine) walls of plant spores and pollen grains. It is chemically very stable and has been described as the "toughest material in the plant kingdom". It is well preserved in soils and sediments and with it surviving in spores from the mid‐Ordovician (475 million years ago) providing the earliest evidence of plant life on land.