Upchurch, Garland R.2007-11-062012-02-241984-02Upchurch, G. R. (1984). Cuticular anatomy of angiosperm leaves from the lower Cretaceous Potomac Group. I Zone I Leaves. American Journal of Botany, 71(2), pp. 192-202.https://hdl.handle.net/10877/2569Angiosperm leaf cuticles from the oldest part of the Potomac Group reinforce previous paleobotanical evidence for a Cretaceous flowering plant diversification. Dated palynologically as Zone I of Brenner (Aptian?), these remains show a low structural diversity compared to later Potomac Group and modem angiosperms. All cuticle types conform to a single plan of stomatal construction that is unusual in its extraordinary plasticity: both the number of subsidiary cells and their arrangement vary greatly on a single epidermis, such that the stomatamight be classified as paracytic, anomocytic, laterocytic, and intermediate. Such stomatal diversity is uncommon in extant angiosperms but is known from a few Magnoliidae. Many species possess secretory cells comparable to the oil cells of modem Magnoliidae, and a few show the bases of probable uniseriate hairs. None of the cuticle types can be assigned to a single modem family, but several show similarities with Chloranthaceae and Illiciales. These results support the concept that subclass Magnoliidae includes some of the most primitive living angiosperms.Text11 pages2 files (.pdf)enCretaceousangiospermscuticlestomataanitaPotomac groupangiospermChloranthaceaeillicialesBiologyArticlehttps://doi.org/10.1002/j.1537-2197.1984.tb12503.x