Enigmatic stems – Hermanophyton

The genus Hermanophyton belongs to a small group of presumable gymnosperms, the Hermanophytales, of which only the stems are known to date. Until recently, fossils of these plants were known exclusively from the Upper Jurassic (c. 150 million years ago) of Colorado and Utah, U.S.A. However, more recent records from the Upper Cretaceous (c. 84 million years ago) of Germany demonstrate that these plants also occurred in Europe. 

All Hermanophyton specimens on display here show the characteristic structure of the stem, which is not found in any other plant group. The stems consist of wedge-shaped wood segments arranged radially around a central pith. The individual segments, in which cells are arranged in rows, are separated from each other by wide spaces of non-woody cells. The wood is surrounded by a thick, multi-layered bark of thin-walled cells and thick-walled fibers. The periphery consists of dead, thick-walled cells, and can perhaps best be compared with the bark of modern trees. 

Since Hermanophyton stems could become very long (the longest specimen is c. 10 m long), but rarely reached diameters of more than 15 cm, and because the stems are almost always unbranched, some have assumed that these plants were lianas. However, there is at least one unusually large Hermanophyton stem from the Jurassic of Colorado, a slice of which can also be seen here. This fossil calls the liana hypothesis into question. Due to the diameter and the massive bark, it is difficult to envision that the plant that produced this stem was a liana. It could also be that there were both tree- and liana-like representatives within the genusHermanophyton.

The systematic position of the Hermanophytales has not yet been resolved. In the broadest sense, they are probably related to the cycads (Cycadales) or bennettites (Bennettitales).