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 Early 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''.H. Kerp, N.H. Trewin and H. Hass (2004) New gametophytes from the Early Devonian Rhynie chert. Transactions of the Royal Society of Edinburgh, Earth Sciences, 94, 411–428 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 of the gametophytes 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 late friend and colleague, the botanist David Thomas Gwynne-Vaughan.

A study of the vascular tissue of the two by David S. Edwards in 1986 lead to the conclusion that the cell walls of the water-conducting cells of ''R. major'' lacked the secondary thickening bars seen in the xylem of ''R. gwynne-vaughanii'', and were more like the water-conducting hydroids 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 ''Aglaophyton'', leaving ''R. gwynne-vaughnii'' as the only known 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).

References

{{Taxonbar, from=Q310514

Early Devonian plants
Prehistoric plant genera