The Late Devonian Red Hill locality in Clinton County, north-central Pennsylvania has yielded an Archaeopteris-dominated plant fossil assemblage that includes cormose lycopsids, seed cupules, sphenopteroid whole-plants, and Barinophyton citrulliforme. The genus Archaeopteris is represented at Red Hill by the foliage species A. macilenta and A. hibernica. The seed cupules of Red Hill are contemporaneous with the earliest known grade of gymnospermous evolution. Palynological analysis of the Red Hill deposits has revealed an age of Fa2c, like that of the Elkinsia beds in Elkins, West Virginia. The Red Hill cupules are similar in morphology to those of Elkinsia, but exhibit a greater degree of fusion of the cupule quadrants. Lycopsids are mainly represented at Red Hill by numerous axes, many of which came from plants that were the size of small shrubs. Included among these axes are specimens with cormose bases and attached rootlets. A large terminal axis fragment (10 cm) of Barinophyton citrulliforme has come out of the same bedding plane as the seed cupules. It has five alternately-arranged strobili that are smaller in size toward the distal end of the axis. There are several specimens of a fern or seed-fern with sphenopteroid foliage from Red Hill that include attached stems and roots. Red Hill is an outcrop of the Duncannon Member of the Catskill Formation. The kilometer-long exposure represents an array of fluvial facies from floodplain to channel deposits, in addition to floodplain paleosols. Together with its relatively diverse plant fossil assemblage, the sediments and paleosols of the Red Hill outcrop are conducive to a detailed reconstruction of the landscape in which grew a Late Devonian subtropical lowland Archaeopteris forest.

Key words: Archaeopteris, Barinophyton citrulliforme, Devonian, Isoetales, Lycopsida, Spermatopsida, Sphenopteris