Carboniferous Horsetails

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 pith casts.
 

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.