History of botany scope of the subject as technology has opened up new techniques and areas of study. Modern molecular systematics, for example, entails the principles and techniques of taxonomy, molecular biology, computer science and more. Within botany there are a number of sub-disciplines that focus on particular plant groups, each with their own range of related studies (anatomy, morphology etc.). Included here are: phycology (algae), pteridology (ferns), bryology (mosses and liverworts) and palaeobotany (fossil plants) and their histories are treated elsewhere (see side bar). To this list can be added mycology, the study of fungi, which were once treated as plants, but
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