Horneophyton in Rhynie chert
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Photograph: Rhynie chert, level bands in cavities indicating the orientation,
poorly preserved upright Horneophyton shoots, shrunk and crumpled, one with forking central strand,
    another shoot upset, pointing downward with sporangium at the top,
    two lobes with columella seen here, other ones possibly cut away or hidden in the depth.

Horneophyton is distinguished by at least three unique features:
1. Its sporangia are of such an irregular and variable shape that nobody seems to be able to tell whether they should be regarded as several sporangia fused into one or as one sporangium branching into several lobes, every one with its separate small opening.
2. There is a kind of central stalk inside the sporangium, called columella, which is branched like the sporangium itself.
Horneophyton grows tubers, often in a string where they can fuse laterally into a short rhizome.

ad 1: Contrary to evidence, Horneophyton sporangia are usually pictured with neat regular shapes [1], Fig.8.40.
For details see  Rhynie Chert News 15.
ad 2: A distinct columella inside the sporangium is a charactersitic feature of the hornworts. In the case of Aglaophyton, the central strand of the stalk extends a little bit into the sporangium where it forms a small mound. It is not known whether the columella in Horneophyton and hornworts and the mound in Aglaophyton are mutually related in a phylogenetic sense.
ad 3: Horneophyton is still described as having a tuber [1] although it has become known that
often it has got a rhizome consisting of adjacent tubers [2].
For more about these tubers see Rhynie Chert News 27, 79, 81.
For Horneophyton spore tetrads see Rhynie Chert News 45, 150.
Note also the corrections under the heading "Errors".    

H.-J. Weiss              last updated 2016, 2019

[1]  T.N. Taylor, E.L.Taylor, M. Krings: Paleobotany, Elsevier 2009.
[2]  H. Hass, H. Kerp:  Rhynie chert plants and their substrates. Conference "The Rhynie Hot Spring System", Aberdeen 2003.

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