The genera Lepidodendron, Sigillaria, Stigmaria, or Calamites, which played so great a share in the vegetation of the same age in the northern hemisphere, have not been recognized among the Palaeozoic forms of India, but examples of Sigillaria, Lepidodendron and Bothrodendron are known to have existed in South Africa in the Permo-Carboniferous era.
In New South Wales, for example, we have such genera as Rhacopteris and Lepidodendron represented by species very similar to those recorded from Lower Carboniferous or Culm rocks in Germany, Austria, England, Spitzbergen, North and South America and elsewhere.
The anatomy of Lepidodendron and its immediate allies is now well known in a number of species; the Carboniferous rocks of Great Britain are especially rich in petrified specimens, which formed the subject of Williamson's extensive investigations.
In Sigillaria the latter form vertical rows, while in Lepidodendron the arrangement is a complicated spiral.
The genus Bothrodendron, going back to the Upper Devonian, differs from Lepidodendron in its minute leaf-scars and the absence of leafcushions, the scars being flush with the smooth surface of the stem.
The cones of Lepidodendron and its immediate allies are for the most part grouped under the name Lepidostrobus.
This order includes only, extinct forms, the best known of which are the plants placed in the genera Lepidodendron and Sigillaria.
For example, the form and structure of Stigmaria have long been well known; but it is seldom possible to determine whether a given Stigmaria belonged to Sigillaria, Lepidodendron or some other genus.
The same is the case in Lepidodendron obovatum, one of the few species in which both external and internal characters are known.
In the cone attributed to the Lower Carboniferous Lepidodendron Veltheimianum) the arrangement was that usual in Selaginella, the microsporangia occurring above and the megasporangia below in the same strobilus (diagram, fig.