Psaronius: a Carboniferous tree-fern

Although the overall aspect of a Carboniferous swamp forest was dominated by arborescent lycopods, ferns made up a significant component of the vegetation. On these ferns, the most spectacular was a large tree-fern, Psaronius, shown as A in the reconstruction above.
 

These living Cyathea tree ferns from New Zealand give some sense of how a grove of Psaronius may have appeared in life.
 

Since most stumps of this plant (the part to which the name Psaronius is officially applied) are found with their bases imbedded in coal, we assume the plant was normally growing in the swamp peat. This fine reconstruction of the entire plant (Morgan, 1959) shows the straight false trunk, largely composed of adventitious roots, topped by a magnificent crown of leaves. Mature plants reached a height of 10-15 meters.
 

Here is a cross-section of a petrified Psaronius trunk (Morgan, 1959), high up the plant and very close to the crown of leaves. A modest number of adventitious roots can be seen on the outside (especially at the top), but most of the outer area is made up of very large leaf bases. The intricate stele, the true stem, is made up or a great many arcs representing intricate xylem bundles. As you would move down such a stem toward the base, the proportion of roots would increase and the stem would get smaller. At the base of the false trunk, you would typically see the entire structure was made up of roots with little or no stem tissue.
 

A reconstruction (Stidd, 1971) showing one of the many compound fronds that make up the crown of leaves at the apex of the trunk. These particular leaves bear sporangia and are of the Scolecopteris type.
 

Here is a nice specimen of Pecopteris (Janssen, 1957), the form genus most commonly used for sterile foliage of the Psaronius type. This specimen represents one of the last units in the complex compound frond system (see the previous reconstruction by Stidd).

Psaronius-type tree ferns briefly assumed dominance at the very end of the Carboniferous with the decline in the importance of arborescent lycopods. The genus became extinct in the Permian, although smaller ferns in the same family are still found today in the tropics.