Department of Plant Biology and Department of Geological Sciences
Michigan State University
Living horsetails are limited to a single genus - Equisetum, none of which a typically more than a meter in height. Whorled parts, including branches, leaves, and cone scales are characteristic of living and extinct horsetails. Note the characteristic terminal, spore-bearing cone on the left. The whorled structures on the stem of this specimen are small branches. The very small whorled leaves at the nodes of the branches are barely visible.
A reconstruction of a Carboniferous swamp forest (Field Museum, Chicago). The large plant in the extreme right foreground is Calamites, an arborescent horsetail. Not so obvious, are viney Sphenophyllum plants that formed part of the tangle of underbrush.
Right, a reconstruction of a Calamites (Hirmer,
1927). Although one erect stem is shown here, the plants typically grew
in clumps like modern bamboo. Left, a cross section of a Calamites
stem (Seward, 1898), showing the large pith cavity and the ridges of xylem
that produce the longitudinal striations on typical Calamites
Palaeostachya, one of the several form genera
for cones borne by Calamites (Stewart, 1983).
Annularia, one of the foliage types produced
by Calamites (Stewart, 1983). The leaves, like all the parts
in this group of plants are whorled.
A reconstruction of Spenophyllum emarginatum
from the Field Museum in Chicago. Most Sphenophyllum plants
had a more vine-like aspect.
Ralph E. Taggart (email@example.com)