Pollen grains of flowering plants are protected because of a stable, rot-resistant outer rind.

References

"The outer rind that carries [pollen grains] is composed of a substance so stable and so resistant to rotting that it may survive for tens of thousands of years and still be recognisable." (Attenborough 1995:95)

Book
The Private Life of PlantsBBC BooksAugust 21, 1995
David Attenborough

Living System/s