Horneophyton rhizome  
deutsche Version

In the scientific literature on the early land plants found in the Lower Devonian Rhynie chert,
Horneophyton is most often pictured by drawings which had not been drawn after fossil evidence but after previous drawings, with slight modifications for copyright reasons. The repeated re-drawing occasionally produced grossly disproportionate shapes. Also it confirmed the impression that structures originally meant to be schematic illustrations [1] were close to reality. This has concisely been laid out, together with related literature, under the heading "Errors and mistakes", Part "Poor reconstructions". Horneophyton rhizome of 6 fused tubers

As a well-known fact,
Horneophyton is distinguished by three peculiar features: the odd-shaped sporangia on top, the branching columella therein, and the perennial tubers in the ground. Apparently they served the same purpose as the onions of flowering plants do nowadays, and often have similar shapes, but unlike onions they do not have a shell structure. Their typical width is up to 4mm, corresponding to the small size of the plant. Their mutual arrangement and their possible connectivity are not easily derived from cut faces.
A drawing in an early publication [2] shows 3 tubers apparently grown one after another in a row, the last one bearing the currently alive small stem. According to a drawing in [1], several tubers may be laterally fused in irregular ways, every one with a stem. Tubers with stems grown in a straight string had been shown in [3] and interpreted there as a kind of straight rhizome.
An own sample provides a string of 6 tubers, closely fused in a horizontal plane such that the shape resembles that of a horseshoe. With a rhizome like this, the plant would less easily topple on soft waterlogged ground.
The lateral fusion had gone rather far here so that the tubers do not appear as individual entities, which differs remarkably from the aspect of the apparently individual tubers also found in the Rhynie chert (see Rhynie Chert News 27). It would be interesting to know whether or not there is a meaning to the differing mutual connectivity of the tubers of this enigmatic plant which apparently lacks any relatives that could help to find for it a branch on the phylogenetic Tree of Life.

Photograph: Horneophyton rhizome in Rhynie chert, consisting of 6 tubers fused into a horseshoe-shaped object, cut nearly horizontally.  Width of the picture 10mm.

 H.-J. Weiss       2015

[1]  D.A. Eggert: The sporangium of Horneophyton lignieri.  Amer. J. Bot. 61(1974), 405-413.
[2]  R. Kidston, W.H. Lang: On Old Red Sandstone plants showing structure, ... Part IV, Trans. Roy. Soc. Edinburgh 52(1921), 831-54.
[3]  H. Hass, H. Kerp:  Rhynie chert plants and their substrates.  "The Rhynie Hot Spring System" Conference,  Aberdeen 2003.
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