Marattialean tree fern (pecopterid) foliage is a major component of fossil adpression floras of Late Pennsylvanian and Early Permian age in north-central Texas. Thus, identification of pecopterid species is important in studies of vegetational responses to changing climatic conditions. Species affinities, however, always have been difficult to determine because most specimens are fragmentary and represent terminal or peripheral portions of fronds where character-state variation is low. Diversity at any single collecting site is high, obscuring boundaries between recurrent morphotypes if floristic analyses are carried out site-by-site. To overcome these difficulties, specimens with similar pinnule shape, venation, lobing characteristics, terminal pinnule morphology, and pinnule-pinna morphometric relationships were grouped independently of collecting locality and stratigraphic position. Once morphotype descriptions and suites of characteristic specimens were assembled, collections were reexamined site by site and the component pecopterids identified. In the Late Pennsylvanian, pecopterid diversity at any site may exceed 10 morphotypes. This site-level diversity declines on-average in the Early Permian. Fourteen morphotype groups were identified in the Late Pennsylvanian (Virgilian). Eight additional groups were found in the early Early Permian (Wolfcampian), along with a number of persistent Pennsylvanian forms. A preliminary assessment of the late Early Permian (Leonardian) indicates the first appearance of additional morphotypes. Several of the foliage morphotypes appear to correspond to described species: Pecopteris ameromii, P. arborescens, P. bucklandii, P. palacea, P. polymorpha, P. puertollanensis, P. unita, P. vera. Based on pinnule venation, others can be assigned to the polymorphopterid or lobatopterid groups of R.H. Wagner. Final species determinations are still to be made for most morphotypes. Morphological variability, fragmentary preservation, and high intrinsic diversity lead to the conclusion that the pecopterid nightmare is likely to continue into the foreseeable future.

Key words: fern, Marattiales, Pennsylvanian, Permian, systematics