''Rhynia'' is a single-species genus of

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wh ...

vascular plants. ''Rhynia gwynne-vaughanii'' was the

sporophyte A sporophyte () is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase. Life cycle The sporophyte develops from the zygote ...

generation of a vascular, axial, free-sporing diplohaplontic embryophytic land plant of the Early Devonian that had

anatomical Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having it ...

features more advanced than those of the

bryophyte The Bryophyta s.l. are a proposed taxonomic division containing three groups of non-vascular land plants (embryophytes): the liverworts, hornworts and mosses. Bryophyta s.s. consists of the mosses only. They are characteristically limited in s ...

s. ''Rhynia gwynne-vaughanii'' was a member of a

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to all other eutracheophytes, including modern vascular plants.

Description

''Rhynia gwynne-vaughanii'' was first described as a new species by

Robert Kidston Dr Robert Kidston, FRS FRSE LLD (29 June 1852 – 13 July 1924) was a Scottish botanist and palaeobotanist. Life He was born in Bishopton House in Renfrewshire on 29 June 1852 the youngest of twelve children of Robert Alexander Kidston, a Gl ...

and William H. Lang in 1917. The species is known only from the

Rhynie chert The Rhynie chert is a Lower Devonian sedimentary deposit exhibiting extraordinary fossil detail or completeness (a Lagerstätte). It is exposed near the village of Rhynie, Aberdeenshire, Scotland; a second unit, the Windyfield chert, is located ...

Aberdeenshire Aberdeenshire ( sco, Aiberdeenshire; gd, Siorrachd Obar Dheathain) is one of the 32 council areas of Scotland. It takes its name from the County of Aberdeen which has substantially different boundaries. The Aberdeenshire Council area inclu ...

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to ...

, where it grew in the vicinity of a

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...

-rich

hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...

. ''Rhynia'' was a vascular plant, and grew in association with other vascular plants such as '' Asteroxylon mackei'', a probable ancestor of modern

clubmoss Lycopodiopsida is a class of vascular plants known as lycopods, lycophytes or other terms including the component lyco-. Members of the class are also called clubmosses, firmosses, spikemosses and quillworts. They have dichotomously branching ...

es ( Lycopsida), and with pre-vascular plants such as ''

Aglaophyton major ''Aglaophyton major'' (or more correctly ''Aglaophyton majus'') was the sporophyte generation of a diplohaplontic, pre-vascular, axial, free-sporing land plant of the Lower Devonian (Pragian stage, around ). It had anatomical features intermedia ...

'', which is interpreted as basal to true vascular plants. ''Rhynia'' is thought to have had

deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, ...

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 A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the ...

generation A generation refers to all of the people born and living at about the same time, regarded collectively. It can also be described as, "the average period, generally considered to be about 20–⁠30 years, during which children are born and gr ...

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 ''Aglaophyton major'' (or more correctly ''Aglaophyton majus'') was the sporophyte generation of a diplohaplontic, pre-vascular, axial, free-sporing land plant of the Lower Devonian (Pragian stage, around ). It had anatomical features intermedi ...

major'', '' Horneophyton lignieri'' and '' Nothia aphylla'' the gametophytes of ''Rhynia'' were dioicous, bearing male and female gametangia ( antheridia and

archegonia An archegonium (pl: archegonia), from the ancient Greek ''ἀρχή'' ("beginning") and ''γόνος'' ("offspring"), is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female ga ...

) 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

s. His conclusion was that ''R. gwynne-vaughanii'' belongs in the vascular plants, while ''R. major'' belongs among the

s. Accordingly, he transferred it to a new genus ''

'', 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 A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

for the polysporangiophytes, in which ''Rhynia'' and the other Rhyniaceae are placed as basal

vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...

s (tracheophyes).

References

{{Taxonbar, from=Q310514 Early Devonian plants Prehistoric plant genera