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The flowering plants Pteridophyta constitute the largest and most diverse group of vascular plants after the flowereing plants. Ferns, like mosses and lycophytes are spore plants , but differ from these groups because ferns have true " leaves " (named megaphylls). These feathers or leaves are usually feather-like and differ in terms of structure from the leaves of seed plants. Ferns exhibit a wide variety of growth forms. Some herbaceous species grow upright (e.g. Matteuccia struthiopteris), while others have a creeping rhizome and so can cover large areas (e.g. Polypodium vulgare). There are also tree-like ferns (Cyathea cooperi for example).
One of the ways in which modern ferns can be subdivided is on the basis of the type of spores that they produce. Within this division, we have two main groups, namely the eusporangiate and leptosporangiate ferns. Living representatives of the first group can be regarded as living fossils because the bulk of the present living species belongs to the leptosporangiate ferns. The current diversity of forms within the pteridophyta reflects the groups rich history. Below is a brief overview which focuses on groups whose fossils are common finds. Groups with a more limited fossil record are not described here.
The first fern-like plants appeared probably by the end of the Lower Devonian period. Many of these early plants also show characteristics associated with other plant groups (such as the formation of secondary wood) besides fern-like properties. It is therefore not known with certainty which of these plants are precursors of ferns and which are not. The Cladoxylales and Rhacophylales, especially important in the Middle Devonian flora, are examples of such uncertain groups. By the Late Devonian appeared Zygopteridales and Stauropteridales. These groups are generally not described as 'true' ferns, but it is included in the fern group. During the further course of the paleozoic all four groups became extinct and were replaced by more advanced ferns.
Rhacophyton cordrusorum (Rhacophyta) Devonian, Belgium
Alloiopteris, a genus which belongs to the Zygopteridales
During the Carboniferous various types of ferns developed, including the first tree shaped Marattiales (an order of eusporangiate ferns, still know by todays representatives). This tree ferns could grow up to eight meters high. Preserved structural pieces of the stem are known under the name Psaronius, and also the complete plant is often named like this. Leaf prints of Pecopteris, a type foliage associated with Psaronius, are common fossils from the Upper Carboniferous. In Carboniferous rock, fossils of smaller, herbaceous ferns, often with strongly lobed or deeply cut pinnules (leaflets) are also common. The biological affinity of this type of ferns such as Sphenopteris, Renaultia, Crossotheca, and Zeilleria, in many cases is not (yet) exactly known.
Cladophlebis denticulata (Osmundales) Jurassic, Iran
Osmunda illiaensis (Osmundales) Miocene, Austria
Many of today's fern families developed in the aftermath of the Permian-Triassic extinction. The Triassic itself was largely a period of recovery, but at the beginning of the Middle Jurassic most ferns known from todays living representatives allready existed, such as the Dipteridaceae, Matoniaceae and Cyatheaceae. But also the Osmundales and Marratiales were still well represented. Furthermore, we see in the Triassic and Jurassic the first Schizaceae and Dicksoniaceae (The prehistoric-looking present tree fern Dicksonia belongs to this group). In some cases, the fossil forms exhibit this many features in common, that they can not only be placed in a modern family, but can be placed in a present living genus. Fossil Osmunda and Marratia are known from the Cretaceous period.
Tempskya is an exception. This tree fern from the Lower Cretaceous of the northern hemisphere formed a so-called false trunk. This false trunk consisted completely of entangled stems and aerial roots, in contrast to the other species of tree ferns (which formed a root sheath). The foliage was small and did not form a crown as in modern tree ferns, but grew over a large portion of the stem. We know Tempskya only from fossilized pieces of false trunk. Leaves and reproductive structures have never been found as fossils. However, the growth structure of Tempskya is so unique that it placed in its own family, the Tempskyaceae.
The time immediately after the Cretaceous-Paleocene extinction was a (brief) heyday for the ferns. During the ten to one hundred thousend years it took for the flowering plants to recover from the blow, the flora was dominated by ferns. Many of the most modern fern families (e.g. Polypodiaceae, except a few Mesozoic records) developed further in that period and in the Paleocene.
Photos or locations of Sphenophyta at this site
Photos or locations of Other Pteridophyta at this site
Note 1: According to the latest insights obtained from DNA studies, the horsetails (Equisetum for example) belong to the Pteridophyta. However, because the appearance of these plants is very different from the "typical fern", they are placed under the Sphenophyta in our Identification System, which makes identification hopefully easier.
Note 2: For the identification of fern-like leaf fossils, it may be useful to also consult the pages of Pteridospermophyta. These plants are also known as "seed ferns", since the foliage is very similar to that of ferns.
Thanks to Tim Wolterbeek for writing this text. English translation by Herman Zevenberg.
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