Rhynia

Rhynia is a single-species genus of Devonian vascular plants. "Rhynia gwynne-vaughanii" was the sporophyte generation of a vascular, axial, free-sporing diplohaplontic embryophytic land plant of the Lower Devonian that had anatomical features more advanced than those of the bryophytes. "Rhynia gwynne-vaughanii" was a member of a sister group to all other eutracheophytes, including modern vascular plants.
Description.
"Rhynia gwynne-vaughanii" was first described as a new species by Robert Kidston and William H. Lang in 1917. The species is known only from the Rhynie chert in Aberdeenshire, Scotland, where it grew in the vicinity of a silica-rich hot spring. "Rhynia" was a vascular plant, and grew in association with other vascular plants such as "Asteroxylon mackei", a probable ancestor of modern clubmosses (Lycopsida), and with pre-vascular plants such as "Aglaophyton major", which is interpreted as basal to true vascular plants. 
"Rhynia" is thought to have had deciduous lateral branches, which it used to disperse laterally over the substrate and stands of the plant may therefore have been clonal populations.
Evidence of the gametophyte generation of "Rhynia" has been described in the form of crowded tufts of diminutive stems only a few mm in height, with the form genus name "Remyophyton delicatum". Like those of "Aglaophyton major", "Horneophyton lignieri" and "Nothia aphylla" the gametophytes of "Rhynia" were dioicous, bearing male and female gametangia (antheridia and archegonia) on different axes. A significant finding is that the axes were vascular, unlike almost all of the gametophytes of modern pteridophytes except for that of "Psilotum".
Taxonomy.
Two species of "Rhynia" were initially described by R. Kidston and W. H. Lang from the Rhynie chert bed: "R. gwynne-vaughnii" in 1917, and "R. major" in 1920. "R. gwynne-vaughanii" was named by Kidston and Lang in honour of their former colleague, the botanist Helen Gwynne-Vaughan.
A study of the vascular tissue of the two by David S. Edwards in 1986 lead to the conclusion that the cell structure of "R. major" lacked secondary thickening bars seen in the xylem of "R. gwynne-vaughanii", and was more like the water-conducting system (hydrome) of moss sporophytes. His conclusion was that "R. gwynne-vaughanii" belongs in the vascular plants, while "R. major" belongs among the bryophytes. Accordingly, he transferred it to a new genus as "Aglaophyton", leaving "R. gwynne-vaughnii" as the only species of "Rhynia". "Rhynia" is the type genus for the rhyniophytes, established as the subdivision Rhyniophytina by Banks, but since treated at various ranks.
Phylogeny.
In 2004, Crane et al. published a cladogram for the polysporangiophytes, in which "Rhynia" and the other Rhyniaceae are placed as basal vascular plants (tracheophyes).