Rhynia
Encyclopedia
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 bryophyte
s, and was basal to modern vascular plants or eutracheophytes.
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 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 are 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
.
major by D.S. Edwards in 1986, leaving R. gwynne-vaughnii as the only species. Rhynia is the type genus for the rhyniophytes, established as the subdivision Rhyniophytina by Banks, but since treated at various ranks.
for the polysporangiophyte
s, in which Rynia and the other Rhyniaceae are placed as basal vascular plant
s (tracheophyes).
Sporophyte
All land plants, and some algae, have life cycles in which a haploid gametophyte generation alternates with a diploid sporophyte, the generation of a plant or algae that has a double set of chromosomes. A multicellular sporophyte generation or phase is present in the life cycle of all land plants...
generation of a vascular, axial, free-sporing diplohaplontic
Alternation of generations
Alternation of generations is a term primarily used in describing the life cycle of plants . A multicellular sporophyte, which is diploid with 2N paired chromosomes , alternates with a multicellular gametophyte, which is haploid with N unpaired chromosomes...
embryophytic
Embryophyte
The land plants or embryophytes, more formally Embryophyta or Metaphyta, are the most familiar group of plants. They are called 'land plants' because they live primarily in terrestrial habitats, in contrast with the related green algae that are primarily aquatic. The embryophytes include trees,...
land plant of the Lower Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
that had anatomical
Plant anatomy
Plant anatomy or phytotomy is the general term for the study of the internal structure of plants. While originally it included plant morphology, which is the description of the physical form and external structure of plants, since the mid-20th century the investigations of plant anatomy are...
features more advanced than those of the bryophyte
Bryophyte
Bryophyte is a traditional name used to refer to all embryophytes that do not have true vascular tissue and are therefore called 'non-vascular plants'. Some bryophytes do have specialized tissues for the transport of water; however since these do not contain lignin, they are not considered to be...
s, and was basal to modern vascular plants or eutracheophytes.
Description
R. gwynne-vaughanii was first described as a new species by Kidston and Lang in 1917. The species is known only from the Rhynie chertRhynie chert
The Rhynie chert is an Early Devonian sedimentary deposit exhibiting extraordinary fossil detail or completeness . It is exposed near the village of Rhynie, Aberdeenshire, Scotland; a second unit, the Windyfield chert, is located some 700 m away...
in Aberdeenshire
Aberdeenshire
Aberdeenshire is one of the 32 unitary council areas in Scotland and a lieutenancy area.The present day Aberdeenshire council area does not include the City of Aberdeen, now a separate council area, from which its name derives. Together, the modern council area and the city formed historic...
, Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
, where it grew in the vicinity of a silica-rich hot spring
Hot spring
A hot spring is a spring that is produced by the emergence of geothermally heated groundwater from the Earth's crust. There are geothermal hot springs in many locations all over the crust of the earth.-Definitions:...
. Rhynia was a vascular plant, and grew in association with other vascular plants such as Asteroxylon mackei
Asteroxylon
Asteroxylon is an extinct genus of plants of the Division Lycopodiophyta known from anatomically preserved specimens in an Early Devonian deposit of chert at Rhynie, Aberdeenshire in North-East Scotland that has been dated at...
, 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 lateral branches, which it used to disperse laterally over the substrate and stands of the plant may therefore have been clonal
Cloning
Cloning in biology is the process of producing similar populations of genetically identical individuals that occurs in nature when organisms such as bacteria, insects or plants reproduce asexually. Cloning in biotechnology refers to processes used to create copies of DNA fragments , cells , or...
populations.
Evidence of the gametophyte
Gametophyte
A gametophyte is the haploid, multicellular phase of plants and algae that undergo alternation of generations, with each of its cells containing only a single set of chromosomes....
generation
Alternation of generations
Alternation of generations is a term primarily used in describing the life cycle of plants . A multicellular sporophyte, which is diploid with 2N paired chromosomes , alternates with a multicellular gametophyte, which is haploid with N unpaired chromosomes...
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
Aglaophyton
Aglaophyton major was the sporophyte generation of a diplohaplontic, pre-vascular, axial, free-sporing land plant of the Lower Devonian . It had anatomical features intermediate between those of the bryophytes and vascular plants or tracheophytes.A. major was first described by Kidston and Lang in...
major, Horneophyton
Horneophyton
Horneophyton, a member of the Horneophytopsida, was an early plant which may form a "missing link" between the hornworts and the Rhyniopsida. It is among the most abundant organisms found in the Rhynie chert.-Description:...
lignieri and Nothia
Nothia
Nothia was a genus of Early Devonian vascular plants whose fossils were found in the Rhynie chert in Scotland. It had branching horizontal underground stems and leafless aerial stems bearing lateral and terminal spore-forming organs . Its aerial stems were covered with small 'bumps' , each...
aphylla the gametophytes of Rhynia are dioicous, bearing male and female gametangia (antheridia
Antheridium
An antheridium or antherida is a haploid structure or organ producing and containing male gametes . It is present in the gametophyte phase of lower plants like mosses and ferns, and also in the primitive vascular psilotophytes...
and archegonia
Archegonium
An archegonium , from the ancient Greek ἀρχή and γόνος , is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female gamete. The archegonium has a long neck canal and a swollen base...
) 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
Psilotum
Psilotum is a genus of fern-like vascular plants, one of two genera in the family Psilotaceae, order Psilotales, and class Psilotopsida...
.
Taxonomy
Two species of Rhynia were initially described by Kidston and Lang from the Rhynie chert bed: R. gwynne-vaughnii in 1917, and R. major in 1920. R. major was transferred to a new genus as AglaophytonAglaophyton
Aglaophyton major was the sporophyte generation of a diplohaplontic, pre-vascular, axial, free-sporing land plant of the Lower Devonian . It had anatomical features intermediate between those of the bryophytes and vascular plants or tracheophytes.A. major was first described by Kidston and Lang in...
major by D.S. Edwards in 1986, leaving R. gwynne-vaughnii as the only species. 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 cladogramCladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
for the polysporangiophyte
Polysporangiophyte
Polysporangiophytes, also called polysporangiates or more formally Polysporangiophyta, are plants in which the spore-bearing generation has a structure of branching stems terminating in sporangia...
s, in which Rynia and the other Rhyniaceae are placed as basal vascular plant
Vascular plant
Vascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the clubmosses, Equisetum, ferns, gymnosperms and angiosperms...
s (tracheophyes).