A review of permineralized seed fern stems of the Upper Paleozoic

Dunn, M. T. (Department of Biological Sciences, Cameron University, Lawton, Oklahoma 73505). A Review of Permineralized Seed Fern Stems of the Upper Paleozoic. J. Torrey Bot. Soc. 133: 20–32. 2006.—Stem morphotaxa continue to be the primary line of evidence for pteridosperm phylogenetic analyses, and the current state of our knowledge of Upper Paleozoic permineralized medullosan and manoxylic lyginopterid stems is reviewed here. Manoxylic Lyginopteridaceae include Lyginopteris, Heterangium, Rhetinangium, Schopfiastrum, Microspermopteris, Trivena, Tetrastichia, Tristichia, Lyginopitys, and Laceya. This group is poorly defined, and cannot be grouped by any as yet known synapomorphy. Four genera are generally included in the Medullosaceae; Medullosa, Colpoxylon, Sutcliffia, and Quaestora, however Colpoxylon should be included in Medullosa. This family is characterized by rachis bases that are vascularized by numerous traces produced at more than one node.