Definitions

dichotomise

Horneophyton

Horneophyton was an early plant which may form a "missing link" between the "rhyniophytes" and hornworts. It is among the most abundant organisms found in the Rhynie chert.

History

Its original generic name Hornea transpired to be a synonym, leading to the plant's renaming.

Morphology

The female gametophyte of the plant has been recognised and described as the form taxon Langiophyton mackiei. It grew to a height of around 6 cm, and was free living.

Early stages of development of the sporophytes of Horneophyton (as of hornworts) may have been dependent on their parent gametophytes for nutrition, but mature specimens have expanded, corm-like bases to their stems that bore rhizoids and appear to be anchored in soil, suggesting a capacity for independent existence after the gametophyte had degenerated. The sporophyte had unornamented axes about 2 mm in diameter with an undivided cortex, and stomata were rare. There was a thin central strand of vascular tissue, reinforced with spiral and reticulate thickenings. They bore terminal sporangia, occasionally branched, which contained a central collumella, analogous to the sporangia of hornworts; however, hornworts' sporangia do not dichotomise.

Habitat

Horneophyton grew on sandy, organic-rich soil in damp to wet locations. They usually grew as isolated individuals.

Phylogeny

}} }} With vascular tissue but "bryophyte"-like alternation of phases and sporangia, the organism has been considered a missing link between the hornworts and tracheophytes (which molecular data suggest are sister groups).

Features suggesting a close relationship with the hornworts include the form of its sporangia; its corm also resembles the foot of some hornworts. The free living nature of sporophytes, and the fact that they display branching, are marked differences which force it into the stem group.

External links

  • Horneophyton at the University of Aberdeen. Includes images.

References

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