Lyginopteris royalii sp nov from the Upper Mississippian of North America

A new species of the seed fern Lyginopteris is described from a nodule in U pper Mississippian (middle Chesterian-Namurian A) shales of the Fayettevill e Formation in northwestern Arkansas. The pyritized stem is 2-9 cm long and slightly compressed, with a diameter of about 11 x 5 mm, and shows seven d iverging leaf bases. The primary xylem of the specimen is eustelic. Foliar bundles extend through five internodes before entering the rachis bases; th ey do not divide along their trajectory through the stem. Phyllotaxis of th e specimen approaches 2/5. Longitudinally oriented sclerenchyma strands acc ompany the diverging foliar vascular bundles adaxially in the cortex, and a re incorporated in the outer cortex above the level of foliar rachis diverg ence. In contrast to previously described Lyginopteris species, this specie s lacks capitate epidermal glands. A Lyginopteris type rachis with a paired vascular bundle is preserved in the same nodule. Coprolites probably produ ced by oribatid mites are present in different tissues of the stein. The st udy of the leaf trace divergence necessitated the use of a deformation mode l to help reconstruct the original position of the cauline bundles in the c ompressed stele. This occurrence of Lyginopteris confirms earlier reports o f the genus from North America and emphasizes that it was not restricted to Western Europe. (C) 2001 Elsevier Science B.V. All rights reserved.