Rhyniophyta
Status
The Rhyniophytes are a paraphyletic taxon comprising the first vascular land plants (Rhyniopsida) and their morphologically similar, but avascular, cousins. They thus have a key position in the history of life. The coverage includes a brief discussion of their structure and importance on this page. Individual pages are included on two very early forms, Horneophyton and Aglaophyton, as well as on two well-known, derived members of the monophyletic Rhyniopsida, Cooksonia and Rhynia.
Index
Rhyniophyta: this overview page.
Horneophyton: a very simple, dichotomously branching form with terminal sporangia -- may or may not be vascular.
Aglaophyton: a larger (to 60 cm), and apparantly more terrestrial version of Horneophyton -- probably not vascular.
Cooksonia: a Silurian vascular plant.
Rhynia: a very well-known plant from the Rhynie Chert.
The flora that existed in the Upper Silurian to Lower Devonian was probably an assemblage of marsh inhabitants with structural feature transitional between aquatic non-vascular and land vascular plants. Of these, the Rhyniophyta are a small but prominent group that include some of the earliest and most primitive terrestrial plants.
The Early Rhyniophytes
In these very primitive land plants in which there was little differentiation between the different parts. They had simple shoots rise from a creeping axis which hardly differs in structure from the upright shoots themselves. These shoots or stems often branched in a simple manner, forking into two, and then into two again, and sometimes the shoots terminated in spore capsules called sporangia. These ancient plants lacked leaves, seeds, and flowers. Instead of roots they had horizontal stems, connected with the soil by root hairs. The whole plant was generally less than 50 cm in height. At least one form, Taeniocrada is thought to have been aquatic, although whether a transitional forms from fresh water to land or secondarily aquatic is not clear
Included in the rhyniophytes are ancestral forms are the ancestral genus Cooksonia, from the late Silurian to early Devonian (Wenlock to Frasnian). By the Early Devonian more advanced types like Rhynia had evolved. Fossils of Rhynia from Devonian chert of Rhynie in Aberdeenshire, Scotland are so perfectly preserved that the individual cells within the plant tissue is recognizable.
There are also a number of related forms, like Aglaophyton, apparently not even true tracheophytes,
Systematics
The following represents a suggested Linnean classification and time-line for the rhyniophytes and related forms. Not that the most primitive forms are not necessarily the oldest, indicating that either the evolutionary sequence presented here is incorrect, or that a lot of early plant evolution occurred in regions away from conditions allowing fossilization
Subphylum Rhyniophytina
Class not specified
Order not specified
Aglaophyton - Pragian
Class Horneophytopsida
Order Horneophytales
Family
Horneophytaceae - Pragian
Class Rhyniopsida
Order not specified
Cooksonia - Wenlock to Frasnian
other rhyniophyte fossils
Order Rhyniales
Family
Rhyniaceae -
Lochkovian to Emsian
Occurrence
Links
The Biota of Early Terrestrial Ecosystems: The Rhynie Chert - Ongoing research into the stratigraphy, sedimentology and paleontology of an Early Devonian hot spring, by The Rhynie Chert Research Group: Aberdeen See especially The Rhynie Chert Flora
University of California Museum of Paleontology -- Rhynie Chert
Rhynie Research Index - The Rhynie Chert and its Flora.
Rhynie Chert Pictures - includes coverage of the most important flora
LES CORMOPHYTES (=premières plantes terrestres) - Description et évolution des premières plantes terrestres - evolution of early land plants - in French
Early Land Plants
uploaded ATW050928
