Spores

Spores are organic, unicellular products of asexual reproduction. They comprise part of the life cycle of many plants, algae, fungi, and protozoa, and can be classified based on their origin, dispersal/mobility, function, and morphology. They preserve well in the fossil record because many of them are composed of sporopollenin [1] and represent some of the earliest evidence of plant life on land [2-4]. Both spore tetrads and trilete spores were present by the Ordovician [5]; thus, they are incredibly important markers of terrestrialization [6]. In addition to their importance regarding the evolution of plants, they are also used in more modern settings as (paleo)environmental indicators, including salinity [7], and paleoecological [8] and archaeological [9] studies of deposits in marine, peat, soil and lacustrine settings.

Additional resources
http://www.geo.arizona.edu/palynology/ppfspor.html
http://reflexions.ulg.ac.be/cms/c_31026/en/land-plants-have-suddenly-aged?portal=j_55&printView=true

References
1. Steemans, P., Lepota, K., Marshall, C.P., Le Hérisséc, A., Javaux, E.J. 2010. FTIR characterisation of the chemical composition of Silurian miospores (cryptospores and trilete spores) from Gotland, Sweden. Review of Palaeobotany and Palynology, 162, 577–590.

2. Wellman, C.H., Gray, J. 2000. The microfossil record of early land plants. Philosophical Transactions of the Royal Society B, 355, 717.

3. Wellman, C.H., Osterloff, P.L., Mohiuddin, U. 2003. Fragments of the earliest land plants. Nature, 425, 282–285.

4. Steemans, P., Herisse, L., Melvin, J., Miller, A., Paris, F., Verniers, J., Wellman, H. 2009. Origin and Radiation of the Earliest Vascular Land Plants. Science, 324, 353–353.

5. Rubinstein, C.V., Gerrienne, P., De La Puente, G.S., Astini, R.A., Steemans, P. 2010. Early Middle Ordovician evidence for land plants in Argentina (eastern Gondwana). New Phytologist, 188, 365–369.

6. Gray, J., Chaloner, W.G., Westoll, T.S. 1985. The Microfossil Record of Early Land Plants: Advances in Understanding of Early Terrestrialization, 1970-1984. Philosophical Transactions of the Royal Society B, 309, 167–195.

7. Mudie, P., Rochon, A., Aksu, A.E., Gillespie, H. 2002. Dinoflagellate cysts, freshwater algae and fungal spores as salinity indicators in Late Quaternary cores from Marmara and Black seas. Marine Geology, 190, 203-231.

8. van Geel, B., Gelorini, V., Lyaruu, A., Aptroot, A., Rucina, S., Marchant, R., Sinninghe Damsté, J.S., Verschuren, D. 2011. Diversity and ecology of tropical African fungal spores from a 25,000-year palaeoenvironmental record in southeastern Kenya. Review of Palaeobotany and Palynology, 164, 174-190.

9. McAndrews, J.H., Turton, C.I. 2010. Fungal spores record Iroquoian and Canadian agriculture in 2nd millennium A.D. sediment of Cawford Lake, Ontario, Canada. Vegetation History and Achaeobotany, 19, 495-501.