ARCHAEOLEERSIA NEBRASKENSIS GEN. ET SP. NOV. (GRAMINEAE-ORYZEAE), A NEW FOSSIL GRASS FROM THE LATE TERTIARY OF NEBRASKA

Archaeoleersia nebraskensis, gen. et sp. nov. was collected from the Late Miocene Ash Hollow Formation in Garden County, Nebraska. The remains consist of anthoecia (fertile lemmas and paleas) preserved as silicifications. Examination of anthoecia by scanning electron microscopy revealed prickle hairs, simple projections, and microhairs. The fossils compare most closely with living Leersia ligularis Trin. of Central and South America. Archaeoleersia nebraskensis resembles more southern living taxa and suggests that climatic deterioration during the Late Tertiary or Quaternary resulted either in a southward migration of ancestral North American forms or in the elimination of North American populations of already widely distributed ancestral forms. Associated flora and fauna indicate a mesic, lacustrine paleoenvironment for Archaeoleersia nebraskensis.