For the purposes of this intro course we will consider three informal groups of plants, distinguished from each other by their modes of reproduction. The simplest are those vascular plants that reproduce with spores. This actually includes four formal taxa ("divisions", which are the plant equivalent of "phyla"). The simplest spore-bearers are called "psilophytes". They have only green stems and spore cases -- no leaves, no roots. They live in water. Fossils are as nondescript as the recent ones.
Somewhat more complex are the horsetails or Equisetophyta (or Sphenophyta). These have distinctively ribbed green stems with spore cases at the end, and they have true roots, allowing them to live out of water. There are tiny scale-like leaves only at the stem joints. Modern forms are rather small, as can be seen from the picture below, but tree-sized forms 10's of meters in height were common in the Paleozoic. They are easily recognized as equisetophytes by their ribbed stems that reach many cm in diameter. The picture is Equisetum arvense photographed near Franklin, WV. The lens cap is ~4.5 cm in diameter. (Photo by B. Carter)
The next photograph shows a mold of a Pennsylvanian sphenopsid stem along with a couple of stem fragments from modern Equisetum hyemale from near Fort Gaines, GA. Notice the longitudinal ribbing in both species. The scale bar is 1cm. (Photo by B. Carter.)
A little more complex than the horsetails are the clubmosses or Lycophyta. These have true roots, stems, and many small, scale-like leaves that attach to the stems in a characteristic spiral pattern. The first photo below is a modern form found growing in a bog near Moultrie, GA. The plant near the center with the somewhat spiky appearance is the lycopsid, and it stands (and reclines) about 10 cm in height, a typical size for Recent species. (Photo by B. Carter)
The next photo is of a Pennsylvanian fossil form at Desoto Falls near Ft. Payne, AL. The specimen that crosses the photograph horizontally is the lycopsid. The pocket knife is about 9 cm long, so the stem of the fossil is approximately that diameter. This is not particularly large for late Paleozoic lycophytes, which reached 10's of meters of height. The diamond shaped marks on the stem are the leaf attachment scars which allow easy recognition of this taxon. (Photo by B. Carter)
The most common spore-bearing plants presently are the ferns (Pteridophyta), which come in a variety of forms. The pictures below show some of the modern types. Ferns, like lycopsids and horsetails, much more often reached tree-size dimensions in the late Paleozoic. The final picture is a slab with the leaves of several small species on it.
Bird's nest fern in a 10 inch (25 cm) pot. (Photo by B. Carter.)
Staghorn fern. The sweetgum tree from which it hangs is about 30 cm in diameter. (Photo by B. Carter.)
A "typical" fern. The brown dots on the leaf underside are the spore cases. (Photo by B. Carter.)
A piece of Pennsylvanian shale from Durham, GA with fossil fern leaves on it. (Photo by B. Carter.)
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