Glossopteris
Glossopteris is probably the most familiar fossil leaf to nonspecialists. The name Glossopteris is Latinized from two Greek words meaning "tongue-fern", referring to the elongated shape of individual leaves. Glossopteris was not a true fern - it was a seed fern (a group of primitive gymnosperms) (Plantae, Pteridospermophyta, Glossopteridopsida, Glossopteridales, Glossopteridaceae). Glossopteris is reconstructed as a large deciduous tree.
The Australian rock shown below is a commercial specimen with several hematite-stained leaf impressions of Glossopteris browniana Brongniart, 1831 (or Glossopteris indica Schimper, 1874 - I'm not sure which one this is). Glossopteris species taxonomy is notoriously convoluted, with >200 nominal species described worldwide. During the Permian, Glossopteris-dominated forests covered much of the ancient continent of Gondwana (= the modern southern continents of South America & Africa & Antarctica & India & Australia).
Glossopteris leaves in hard deltaic claystone (field of view 12.4 cm across).
This fossil leaf has tremendous significance in the history of geology. The modern-day geographic distribution pattern of Glossopteris fossils was a key piece of paleontological evidence that Alfred Wegener used in formulating his Continental Drift Hypothesis in 1915.
Stratigraphy: Illawarra Coal Measures, mid-Kazanian or Midian/Tatarian or Dzhulfian Stage, Upper Permian.
Locality: Dunedoo, Sydney Basin, eastern New South Wales, southeastern Australia.
Wegener, A. 1915. Die Entstehung der Kontinente und Ozeane. Braunschweig. F. Vieweg. 94 pp. [English translation of 4th edition, 1966: The Origin of Continents and Oceans. 246 pp.]