The rhyniophytes are a group of extinct early
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 al ...
s that are considered to be similar to the genus ''
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 feat ...
'', found in the
Early Devonian
The Early Devonian is the first of three epochs comprising the Devonian period, corresponding to the Lower Devonian series. It lasted from and began with the Lochkovian Stage , which was followed by the Pragian from and then by the Emsian, wh ...
(around ). Sources vary in the name and
rank
Rank is the relative position, value, worth, complexity, power, importance, authority, level, etc. of a person or object within a ranking, such as:
Level or position in a hierarchical organization
* Academic rank
* Diplomatic rank
* Hierarchy
* H ...
used for this group, some treating it as the class Rhyniopsida, others as the subdivision Rhyniophytina or the division Rhyniophyta. The first definition of the group, under the name Rhyniophytina, was by
Banks
A bank is a financial institution that accepts deposits from the public and creates a demand deposit while simultaneously making loans. Lending activities can be directly performed by the bank or indirectly through capital markets.
Because ...
,
since when there have been many redefinitions,
including by Banks himself. "As a result, the Rhyniophytina have slowly dissolved into a heterogeneous collection of plants ... the group contains only one species on which all authors agree: the type species ''Rhynia gwynne-vaughanii''".
When defined very broadly, the group consists of plants with dichotomously branched, naked aerial axes ("stems") with terminal spore-bearing structures (sporangia).
[ The rhyniophytes are considered to be stem group tracheophytes (vascular plants).
]
Definitions
The group was described as a subdivision
Subdivision may refer to:
Arts and entertainment
* Subdivision (metre), in music
* ''Subdivision'' (film), 2009
* "Subdivision", an episode of ''Prison Break'' (season 2)
* ''Subdivisions'' (EP), by Sinch, 2005
* "Subdivisions" (song), by Rus ...
of the division Tracheophyta
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 al ...
by Harlan Parker Banks in 1968 under the name Rhyniophytina. The original definition was: "plants with naked (lacking emergences), dichotomizing axes bearing sporangia that are terminal, usually fusiform and may dehisce longitudinally; they are diminutive plants and, in so far as is known, have a small terete xylem strand with a central protoxylem." With this definition, they are polysporangiophyte
Polysporangiophytes, also called polysporangiates or formally Polysporangiophyta, are plants in which the spore-bearing generation (sporophyte) has branching stems (axes) that bear sporangia. The name literally means 'many sporangia plant'. The cl ...
s, since their 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 p ...
s consisted of branched stems bearing sporangia
A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their lif ...
(spore-forming organs). They lacked leaves or true roots but did have simple vascular tissue
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There ...
. Informally, they are often called rhyniophytes or, as mentioned below, rhyniophytoids.
However, as originally circumscribed
In geometry, the circumscribed circle or circumcircle of a polygon is a circle that passes through all the vertices of the polygon. The center of this circle is called the circumcenter and its radius is called the circumradius.
Not every pol ...
, the group was found not to be monophyletic
In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
since some of its members are now known to lack vascular tissue. The definition that seems to be used most often now is that of D. Edwards and D.S. Edwards: "plants with smooth axes, lacking well-defined spines or leaves, showing a variety of branching patterns that may be isotomous, anisotomous, pseudomonopodial or adventitious. Elongate to globose sporangia were terminal on main axes or on lateral systems showing limited branching. It seems probable that the xylem, comprising a solid strand of tracheids, was centrarch." However, Edwards and Edwards also decided to include rhyniophytoids, plants which "look like rhyniophytes, but cannot be assigned unequivocally to that group because of inadequate anatomical preservation", but exclude plants like ''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 ...
'' and ''Horneophyton
''Horneophyton'' is an extinct early plant which may form a "missing link" between the hornworts and the Rhyniopsida. It is a member of the class Horneophytopsida. ''Horneophyton'' is among the most abundant fossil organisms found in the Rhynie c ...
'' which definitely do not possess tracheids.
In 1966, slightly before Banks created the subdivision, the group was treated as a division under the name Rhyniophyta.[ Taylor et al. in their book ''Paleobotany'' use Rhyniophyta as a formal taxon,][ but with a loose definition: plants "characterized by dichotomously branched, naked aerial axes with terminal sporangia".][ They thus include under "other rhyniophytes" plants apparently without vascular tissue.][
In 2010, the name paratracheophytes was suggested, to distinguish such plants from 'true' tracheophytes or eutracheophytes.]
In 2013, Hao and Xue returned to the earlier definition. Their class Rhyniopsida (rhyniopsids) is defined by the presence of sporangia that terminate isotomous branching systems (i.e. the plants have branching patterns in which the branches are equally sized, rather than one branch dominating, like the trunk of a tree). The shape and symmetry of the sporangia was then used to divide up the group. Rhynialeans (order Rhyniales), such as ''Rhynia gwynne-vaughanii'', ''Stockmansella'' and ''Huvenia'', had radially symmetrical sporangia that were longer than wide and possessed vascular tissue with S-type tracheids. Cooksonioids, such as ''Cooksonia pertoni'', ''C. paranensis'' and ''C. hemisphaerica'', had radially symmetrical or trumpet-shaped sporangia, without clear evidence of vascular tissue. Renalioids, such as '' Aberlemnia'', ''Cooksonia crassiparietilis'' and ''Renalia'' had bilaterally symmetrical sporangia and protostele In a vascular plant, the stele is the central part of the root or stem containing the tissues derived from the procambium. These include vascular tissue, in some cases ground tissue (pith) and a pericycle, which, if present, defines the outermost bo ...
s.[
]
Taxonomy
There is no agreement on the formal classification to be used for the rhyniophytes. The following are some of the names which may be used:
* Division Rhyniophyta
** Subdivision Rhyniophytina Banks (1968)
*** Class Rhyniopsida Kryshtofovich (1925)
**** Order Rhyniales Němejc (1950)
***** Family Rhyniaceae Kidston & Lang (1920)
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 the Rhyniaceae are shown as the sister group of all other tracheophytes (vascular plants). Some other former "rhyniophytes", such as ''Horneophyton'' and ''Aglaophyton'', are placed outside the tracheophyte clade, as they did not possess true vascular tissue (in particular did not have tracheid
A tracheid is a long and tapered lignified cell in the xylem of vascular plants. It is a type of conductive cell called a tracheary element. Angiosperms use another type of tracheary element, called vessel elements, to transport water through the ...
s). However, both ''Horneophyton'' and ''Aglaophyton'' have been tentatively classified as tracheophytes in at least one recent cladistic analysis of Early Devonian land plants.[
Partial cladogram by Crane et al. including the more certain rhyniophytes:]
(See the Polysporangiophyte
Polysporangiophytes, also called polysporangiates or formally Polysporangiophyta, are plants in which the spore-bearing generation (sporophyte) has branching stems (axes) that bear sporangia. The name literally means 'many sporangia plant'. The cl ...
article for the expanded cladogram.)
Genera
The taxon and informal terms corresponding to it have been used in different ways. Hao and Xue in 2013 circumscribed
In geometry, the circumscribed circle or circumcircle of a polygon is a circle that passes through all the vertices of the polygon. The center of this circle is called the circumcenter and its radius is called the circumradius.
Not every pol ...
their Rhyniopsida quite broadly, dividing it into rhynialeans, cooksonioids
''Cooksonia'' is an extinct group of primitive land plants, treated as a genus, although probably not monophyletic. The earliest ''Cooksonia'' date from the middle of the Silurian (the Wenlock epoch); the group continued to be an important comp ...
and renalioids.[ Genera included by Hao and Xue are listed below, with assignments to their three subgroups where these are given.]
* '' Aberlemnia'' (renalioids)
* ''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 ...
'' (rhynialeans)
* '' Caia''
* ''Cooksonia
''Cooksonia'' is an extinct group of primitive land plants, treated as a genus, although probably not monophyletic. The earliest ''Cooksonia'' date from the middle of the Silurian (the Wenlock epoch); the group continued to be an important comp ...
'' (cooksonioids + renalioids)
* '' Culullitheca''
* '' Eogaspesiea'' (= ''Eogaspesia'') (rhynialeans)
* '' Eorhynia''
* '' Filiformorama''
* '' Fusitheca'' (= ''Fusiformitheca'')
* '' Grisellatheca''
* '' Hsua'' (=''Hsüa'') (renalioids)
* ''Huia
The huia ( ; ; ''Heteralocha acutirostris'') is an extinct species of New Zealand wattlebird, endemic to the North Island of New Zealand. The last confirmed sighting of a huia was in 1907, although there was a credible sighting in 1924.
It ...
''
* '' Huvenia'' (rhynialeans)
* '' Junggaria'' (= ''Cooksonella'', ''Eocooksonia'')
* '' Pertonella''
* '' Renalia'' (renalioids)
* '' Resilitheca''
* ''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 feat ...
'' (rhynialeans)
* '' Salopella'' (rhynialeans?)
* '' Sartilmania''
* '' Sennicaulis''
* '' Sporathylacium''
* '' Steganotheca''
* '' Stockmansella'' (rhynialeans)
* '' Tarrantia'' (rhynialeans?)
* '' Tortilicaulis''
* ''Uskiella
''Uskiella'' is a genus of small fossil plants of Early Devonian age (around ). The diagnostic characters are naked axes branching isotomously, terminating in ellipsoidal, vertically elongate flat sporangia which split longitudinally into two va ...
'' (rhynialeans)
It has been suggested that the poorly preserved '' Eohostimella'', found in deposits of Early Silurian age (Llandovery, around ), may also be a rhyniophyte. Others have placed some of these genera in different groups. For example, ''Tortilicaulis'' has been considered to be a horneophyte.
Rhynie flora
The general term "rhyniophytes" or "rhyniophytoids" is sometimes used for the assemblage of plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...
s found in 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 locat ...
Lagerstätte
A Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These for ...
- rich fossil beds in 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 includ ...
, 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 th ...
, and roughly