''Aglaophyton major'' (or more correctly ''Aglaophyton majus'') 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 pr ...

generation of a diplohaplontic, pre-vascular, axial, free-sporing land plant of the

Lower 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, w ...

(Pragian stage, around ). It 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 intermediate between 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 and

vascular plants 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 ...

tracheophytes 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 ...

. ''A. major'' was first described by Kidston and Lang in 1920 as the new species ''Rhynia major''. 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 Subdivisions of Scotland#council areas of Scotland, council areas of Scotland. It takes its name from the County of Aberdeen which has substantially differe ...

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 the ...

, 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 one ...

-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 ...

, together with a number of associated

such as a smaller species ''

Rhynia gwynne-vaughanii ''Rhynia'' is a single-species genus of Devonian vascular plants. ''Rhynia gwynne-vaughanii'' was the sporophyte generation of a vascular, axial, free-sporing Alternation of generations, diplohaplontic embryophyte, embryophytic land plant of the ...

'' which may be interpreted as a representative of the ancestors of modern vascular plants and '' Asteroxylon mackei'', which was an 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 s ...

es (

Lycopsida 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 s ...

Description

The stems of ''Aglaophyton'' were round in cross-section, smooth, unornamented, and up to about 6mm in diameter. Kidston and Lang interpreted the plant as growing upright, to about 50 cm in height, but Edwards has re-interpreted it as having prostrate habit, with shorter aerial axes of about 15 cm height. The axes branched dichotomously, the aerial axes branching at a comparatively wide angle of up to 90°, and were terminated with elliptical, thick-walled sporangia, which when mature, opened by spiral slits, so that the sporangia appear to be spiral in form. Sporangia contained many identical spores (isospores) bearing trilete marks. The spores may therefore be interpreted as meiospores, the product of meiotic divisions, and thus the plants described by Edwards and by Kidston and Lang were diploid, sporophytes. The plant was originally interpreted as a tracheophyte, because the stem has a simple central vascular cylinder or

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 b ...

, but more recent interpretations in the light of additional data indicated that ''Rhynia major'' had water-conducting tissue lacking the secondary thickening bars seen in the xylem of ''Rhynia gwynne-vaughanii'', more like the water-conducting system ( hydrome) of

moss Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta (''sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and hor ...

s. Edwards reinterpreted the species as non-vascular plant and renamed it ''Aglaophyton major''. ''Aglaophyton'' is among the first plants known to have had a

mycorrhiza A mycorrhiza (from Greek μύκης ', "fungus", and ῥίζα ', "root"; pl. mycorrhizae, mycorrhiza or mycorrhizas) is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the plant ...

l relationship with fungi, which formed arbuscules in a well-defined zone in the cortex of its stems. ''Aglaophyton'' lacked

root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the sur ...

s, and like other rootless land plants of the Silurian and early Devonian may have relied on mycorrhizal fungi for acquisition of water and nutrients from the soil. The male

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

of the species has been formally described,Remy, W & Remy, R (1980) ''Lyonophyton rhyniensis'' n.gen. et nov. spec., ein Gametophyt aus dem Chert von Rhynie (Unterdevon, Schottland). Argumenta Palaeobotanica, 6, 37-72 which was assigned to a new

form taxon Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships. Form classification, generally restricted to palaeontology, reflects uncertainty; the goal of sc ...

''Lyonophyton rhyniensis'', but is now properly referred to as an ''Aglaophyton'' gametophyte. The

bears many examples of male and female gametophytes, which are loosely similar in their construction to the sporophyte phase, down to bearing rhizoids.

Taxonomy

''Aglaophyton major'' was first described as ''Rhynia major'' by Kidston and Lang in 1920. In 1986 D.S. Edwards re-examined fossil specimens and reported that they did not contain true

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 ...

, but rather conducting tissue more similar to that of

s. As the diagnosis of ''Rhynia'' was that it was a

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 ...

, he created a new genus, ''Aglaophyton'', for this species. (The other species of ''Rhynia'', ''R. gwynne-vaughanii'', was not affected.) As ''Rhynia major'' the species had been placed in the

rhyniophyte The rhyniophytes are a group of extinct early vascular plants that are considered to be similar to the genus ''Rhynia'', found in the Early Devonian (around ). Sources vary in the name and rank used for this group, some treating it as the class R ...

s, but no alternative higher level classification was proposed for the new genus.

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 d ...

for the

polysporangiophytes Polysporangiophytes, also called polysporangiates or formally Polysporangiophyta, are plants in which the spore-bearing generation (sporophyte) has branching stems (axes) that bear sporangium, sporangia. The name literally means 'many sporangia pl ...

which places ''Aglaophyton'' as a sister of the

(tracheophytes), with the

Horneophytopsida The Horneophytopsida, informally called horneophytes, are a class of extinct plants which consisted of branched stems without leaves, true roots or vascular tissue, found from the Late Silurian to the Early Devonian (around ). They are the simpl ...

being sister to both. The basis of the cladogram is that ''Aglaophyton'' has more developed conducting tissue than the Horneophytopsida, but does not have true vascular tissue.

References

External links

Cladogram
from {{Taxonbar, from=Q137376 Early Devonian plants Prehistoric plant genera