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Unformatted text preview: similarities suggest that ferns and sphenophytes may have shared a common ancestor within the trimerophytes. The Progymnosperms The progymnosperms are an extinct group of free-sporing (nonseed) plants that have fern-like leaves and reproductive structures attached to gymnosperm-like stems with large amounts of wood. Some progymnosperms produced a single type of spore (homospory) while otyhers produced small and large spores, a condition known as heterospory. This latter group may include the ancestors of seed plants. The most famous oif the progymnosperms, Archaeopteris , was first assigned to the ferns. During the 1960s paleobotanist Charles B. Beck convincingly demonstrated that this common late Devonian leaf fossil was actually produced by the same plant that also produced a common Devonian petrified wood known as Callixylon ....
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