On Paleozoic plants from marine strata: Trivena arkansana (Lyginopteridaceae) gen. et sp. nov., a lyginopterid from the Fayetteville Formation (middle Chesterian/Upper Mississippian) of Arkansas, USA.

Five permineralized seed fern stems from the Fayetteville Formation (middle Chesterian/Upper Mississippian) of Arkansas conform to the concept of lyginopterid seed ferns. However, these specimens are unlike all previously reported lyginopterids, and the name Trivena arkansana (Lyginopteridaceae) gen. et sp.

Additional observations on Rhynchosperma quinnii (Medullosaceae): a permineralized ovule from the Chesterian (Upper Mississippian) Fayetteville Formation of Arkansas.

New ovules from the Fayetteville Formation (Upper Mississippian) of Arkansas expand our knowledge of the morphology and anatomy of Rhynchosperma and suggest it was produced by a medullosan seed fern. Rhynchosperma has been described as radially symmetrical with a two-layered integument and vascularization in the integument only. The apical portion of the integument is ribbed; the nucellus is fused to the integument and apically differentiated into a dome-shaped pollen chamber.