The Sphenophytes

The Sphenophytes - similarities suggest that ferns and...

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The Sphenophytes Once dominant elements in the Paleozoic forests, sphenophytes (also known as the equisetophytes) are today relegated to minor roles as stream-side herbaceous plants. The group is defined by their jointed stems, with many extremely small leaves being produced at a node , production of spores in cones borne at the tips of stems, and spores bearing elaters (devices to aid in spore dispersal). The fossil members of this group are often encountered in coal deposits of Carboniferous age in North America and Europe. The first sphenophytes show up during the late Devonian, most likely evolving from some group of the trimerophytes. The Ferns Ferns reproduce by spores from which the free-living bisexual gametophyte generation develops. There are 12,000 species of ferns today, although the fossil history of ferns shows them to have been a dominant plant group during the Paleozoic Era. The first ferns also appear by the end of the Devonian. Some anatomical
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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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The Sphenophytes - similarities suggest that ferns and...

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