The Horneophytopsida, informally called horneophytes, are a class of extinct plants which consisted of branched stems without leaves, true roots or

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. The ...

, found from the Late Silurian to 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, ...

(around ). They are the simplest known

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, i.e. plants with sporophytes bearing many spore-forming organs ( sporangia) on branched stems. They were formerly classified among 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 ...

s, but it was later found that some of the original members of the group had simple vascular tissue and others did not. The group has also been treated as the division Horneophyta. 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 Horneophytopsida are shown as the sister group of all other polysporangiophytes. One other former rhyniophyte, ''

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 intermedia ...

'', is also placed outside the tracheophyte clade, as it 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 th ...

s), although its conducting tissue is more complex than that of the Horneophytopsida.

Phylogeny

Partial cladogram by Crane, Herendeen & Friis 2004, with emphasis on horneophytes. (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

Genera that have been placed in the horneophytes include: * †'' Caia'' Fanning, Edwards & Richardson (1990) * †'' Horneophyton'' Barghoorn & Darrah (1938) (''Hornea'' Kidston & Lang (1920) non Baker (1877); ''Langiophyton'' Remy & Hass (1991) form taxon – female gametophyte) * †'' Tortilicaulis'' Edwards (1979) Other sources place only ''Horneophyton'' in this group, treating ''Caia'' and ''Tortilicaulis'' as actual or possible

References

External links

''Horneophyton'' at the University of Aberdeen

Cladogram
from {{Taxonbar, from=Q1135335 Early Devonian plants Silurian plants Plant classes Wenlock first appearances Early Devonian extinctions Prehistoric plant taxa