Fern fern ("Onoclea sensibilis"). Giant water fern ("Salvinia molesta") is one of the world's worst aquatic weeds. The important fossil fuel coal consists of the remains of primitive plants, including ferns. Ferns have been studied and found to be useful in the removal of heavy metals, especially arsenic, from the soil. Other ferns with some economic significance include: The study of ferns and other pteridophytes is called pteridology. A pteridologist is a specialist in the study of pteridophytes in a broader sense that includes the more distantly related lycophytes. Pteridomania is a term for the Victorian era craze of fern collecting
Evolutionary history of plants such as "Rhynia" preserved in the Rhynie chert is of similar complexity, which is taken to support this hypothesis. By contrast, with the exception of "Psilotum" modern vascular plants have heteromorphic sporophytes and gametophytes in which the gametophytes rarely have any vascular tissue. There is no evidence that early land plants of the Silurian and early Devonian had roots, although fossil evidence of rhizoids occurs for several species, such as "Horneophyton". The earliest land plants did not have vascular systems for transport of water and nutrients either. "Aglaophyton", a rootless vascular plant known from Devonian fossils in the Rhynie chert