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(American Journal of Botany. 2005;92:1131-1140.)
© 2005 Botanical Society of America, Inc.

Paleobotany

A Late Devonian isoetalean lycopsid, Otzinachsonia Beerboweri, gen. et sp. nov., from north-central Pennsylvania, USA1

Walter L. Cressler III2,4 and Hermann W. Pfefferkorn3

2Francis Harvey Green Library, West Chester University, West Chester, Pennsylvania 19383 USA; 3Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6316 USA

ABSTRACT

Compressions and impressions of an isoetalean lycopsid, comprising lower portions of stems, lobed bases, attached rootlets, and rounded rootlet scars, discovered in Late Devonian (Famennian) rocks of Clinton County, north-central Pennsylvania, Appalachian Basin, USA, are here described as Otzinachsonia beerboweri, gen. et sp. nov. These specimens demonstrate unequivocally the existence of the isoetalean lobe-and-furrow rhizomorphic growth pattern as early as the Late Devonian. They were found in an Archaeopteris- and Rhacophyton-dominated flora at Red Hill, an outcrop of the Duncannon Member of the Catskill Formation. The fossils were found in a dark-gray to greenish-gray lenticular siltstone layer that has an average thickness of 1.0 m. This deposit is interpreted as a floodplain pond. The low-energy nature of the deposit and the fine preservation of the intact rootlets of the specimens imply little or no transport. The plants were probably growing along the edge of the floodplain pond with their lower portions submerged for at least part of the year.

Key Words: Catskill Formation • cormose • Devonian • Famennian • isoetalean • lycopsid • Paleozoic • Plantae






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