exine

noun

(L. ex: outside) The outer, decay-resistant, of two layers forming the wall, coat, of certain spores or pollen grains, sporopollenin, an inert polymer; the exine is characteristic for different plant families and genera, and sometimes even for different species; hence it forms the basis for the identification and quantitative analysis of the vegetation composition of peats and other suitable sedimentary deposits dating back many thousands of years; also called exosporium.