Iridopteris eriensis from the Middle Devonian of North America, with Systematics of Apparently Related Taxa

Abstract

A reinvestigation of the permineralized axis I. eriensis Arnold, from type and new material, was conducted as part of a comprehensive study of all members of the Iridopteridineae of Arnold. Apparently, Iridopteris was a highly distinctive Middle Devonian plant with a 5-ribbed mesarch, primary xylem column and apparent bilateral symmetry; simple protoxylem strands, or cavities representing protoxylem strands, grouped in multiples near the tips of primary xylem ribs; traces of 2 distinct sizes; whorled order of trace departure; metaxylem tracheids with circular to elongate elliptical bordered pit pairs with elliptical apertures; and a distinct boundary between stele and cortex apparently comprised of a single layer of cells with dark materials in their lumina. Accumulating evidence suggests that a taxonomically distinct group of Middle and lower Upper Devonian plants has only partially been recognized. The IRIDOPTERIDALES is here established to include the central concept of Arnold''s Iridopteridineae, except for Reimannia, combined with directly comparable components of the Ibykales of Skog and Banks. Members of this new order include Arachnoxylon, Iridopteris, Ibyka and Asteropteris.