Professor Nathorst has described a remarkable Devonian plant, Pseudobornia ursina (from Bear Island, in the Arctic Ocean), which shows affinity both with the Equisetales and Sphenophyllales.
The Equisetales (Horse-tails), the Lycopodiales (Club mosses), the Filicales (Ferns) and Cycadofilices, the Sphenophyllales and Cordaitales.
The most important and best known of the extinct Equisetales are, however, the Calamites (see Palaeobotany: Palaeozoic).
The study of the Sphenophyllales, however, as has been pointed out above, appears to indicate that the Equisetales and Lycopodiales may be traced back to a common ancestry.
Of other Equisetales there are Schizoneura and Phyllotheca; the former first appears in Lower Gondwana rocks as a member of the Glossopteris flora, migrating at a later epoch into Europe, where it is represented by a Triassic species.
A consideration of the characters of both shows that the Psilotales are the nearest living representatives of the Sphenophyllales, while resemblances suggesting actual relationship exist between this group and the Equisetales and Lycopodiales.