Paleoeriocoma (Gramineae, Stipeae) from the Miocene of Nebraska: Taxonomic and Phylogenetic Significance

Abstract

Anthoecia (lemmas and paleas) of the fossil grass Paleoeriocoma hitchcockii Elias from the Late Miocene Ash Hollow Formation of Nebraska and certain living species of Oryzopsis are similar in micromorphological and macromorphological features. This evidence indicates that Paleoeriocoma hitchcockii stock is ancestral to species of Oryzopsis of the North American sections Eriocoma and Oryzopsis (=Euoryzopsis) and possibly some species of Stipa. The occurrence of Nassella and Paleoeriocoma together in the deposits indicates that the genus Nassella has been distinct from the genera Oryzopsis and some Stipa since at least the late Miocene.