作者: Michael T. Dunn , Michael Krings , Gene Mapes , Gar W. Rothwell , Royal H. Mapes
DOI: 10.1016/S0034-6667(02)00254-3
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摘要: Three specimens of a medullosan seed fern stem with attached leaf bases, from the Chesterian Series Arkansas, USA, are earliest unequivocal occurrence genus Medullosa and form basis for new species steinii. The stems have numerous features characteristic vines, including diameters only 2–3 cm in diameter, wide, plate-like rays, relatively wide tracheids, presence cortical spines variable but stelar segments. In M. steinii vascular segment numbers vary two to eight. Primary xylem bundles consist one several protoxylem poles metaxylem abundant parenchyma; each bundle is surrounded by secondary tissue. Leaf traces typically diverge as pairs, resulting separating other at an angle 90–100°. Paired separated wedge tissue, thus producing distinctive mode trace production species. divide repeatedly produce Myeloxylon rachis base configuration margin cortex. Rachis bases decurrent another discontinuous row sclerotic prominent periderm. discovery this plant demonstrates that scrambling climbing ferns were part some communities Mississippian time.