Phillips, Tom L. Department of Botany, University of Illinois at Urbana-Champaign, Champaign, Illinois.
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True ferns which span the Late Devonian through Permian time between the recognizable beginnings of fernlike morphology and the earliest-appearing extant filicalean families (Gleicheniaceae, Osmundaceae). A true fern is a relatively advanced type of vascular land plant with distinct stem, fronds, roots, and foliarborne annulate sporangia. Coenopterid ferns are mostly small and simple in contrast to late Paleozoic tree ferns of the Marattiales. All well-known genera of the Coenopteridales in the Pennsylvanian Period exhibit fronds with circinate vernation (croziers), laminate vegetative foliage, and annulate sporangia. Their stems are mostly protostelic with a few siphonostelic species, and one genus (Zygopteris) has secondary growth. These ferns are better from anatomically preserved specimens, especially from peat beds, than from coalified compressions, but they occurred in a variety of habitats mostly known on Northern Hemisphere continents. Their fronds have distinct vascular strands, useful in identifying genera (Fig. 1).
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