A peculiar way of creeping  -  Aglaophyton reconsidered
deutsche Version

The most common plant in the Rhynie chert, as often pictured lately, forms arches along the ground from which the upright shoots emerge. The arching growth is said to be brought about by upright shoots falling over when becoming unstable with increasing height [1]. This view, perhaps suggested by the aspect of brambles, has not been disputed since the plant formerly known as Rhynia major was re-named Aglaophyton in 1986 [1].
Doubts arise in view of the fact that Aglaophyton does not look limp and slender with upright shoots about 5mm across and with an assumed height of mere 20cm. Extant plants with such measures are rather sturdy. The doubts are confirmed by fossil evidence: From the rare cases where an arch is incidentally cut lengthwise it becomes obvious that such arches can be so small that they cannot be explained by falling over. The drawing in Fig.2 shows how the half arch seen in Fig.1 may be explained by one prong of the forking axis growing downwards. (The down direction in Fig.1 is indicated by rhizoids seen on a cross section near the end of the arch.) Another example is shown in Fig. 3.
Aglaophyton axis with downward bendschematic drawing illustrating the undulating growth of Aglaophytonforking and arching axes of Aglaophyton
Fig.1, far left: Aglaophyton axis turning sharply downward, arch radius about 1cm.

Fig.2, left: Principle of arch
formation without falling over.

  Fig.3, right: In-plane section of arching and forking
  axes incidentally seen on the natural surface of a
  Rhynie chert sample, arch radius about 1.5cm.

A photograph of an upward bend is shown here.

So it can be concluded that Aglaophyton did not fall over as claimed in [1] but grew downwards to touch the ground, grow rhizoids, and turn upwards again. (This conclusion was first presented at the
3rd Chert Meeting, Chemnitz 2004.)
It would be interesting to know if there were or still are other arching creepers applying this peculiar way of propagation invented by Aglaophyton.

H.-J. Weiss     2008

[1] David S. Edwards, Aglaophyton major, a non-vascular land-plant from the Devonian Rhynie Chert,
      Bot. J. Linn. Soc. 93(1986), 173-204.
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