Ventarura cross-section with dark ring insideVentarura
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Among the Higher Plants in the Rhynie chert, Ventarura had been discovered last, and named and described in 2000 [1]. It was assumed to be confined to a separate and narrowly localized variety of the Rhynie chert, named Windyfield chert. (Hence the name of the plant, which means windy field.)
Like the previously discovered Trichopherophyton, Ventarura belongs to the zosterophylls, a group of plants widely distributed in the Lower Devonian. An incurved tip (like that of most ferns) of
Ventarura has been discovered in a small sample found in 1998 and has remained the only one found hitherto. (See Rhynie Chert News  3 .)

The distinctive feature, a concentric tube with well seen cellular structure while all other tissue had virtually vanished, is found only in the upper parts of the plant which seem to be less often preserved. This tube, seen as a ring on cross-sections with rugged contour, is often but not always conspicuous for its apparently strong cell walls with dark stain. Its original interpretation as sclerenchyma [1] is questionable. (See  Rhynie Chert News 60 , 82.) 
Ventarura parts without a ring on cross-sections are usually not recognized as such. Even Ventarura sections with ring may escape notice if the outline is not rugged but smoothly circular and the cell walls are not stained dark but pale. (See Rhynie Chert News 58.)
One or more younger shoots inside an older one most probably indicate a zosterophyll. (See
Rhynie Chert News 16.)
  
Hollow straws of Aglaophyton with several layers of well-preserved cells below the surface may easily be (and really had been) mistaken for Ventarura. (See  Rhynie Chert News 66 .)
In order to tell Ventarura from Aglaophyton cross-sections, the following rules can be helpful:
It is Ventarura if the ring of well-seen cells is ...
 ... (nearly) circular but the outline of the section is rugged,
 ... well away from the outline,

 ... not continuous or only partial.
It is virtually never
Ventarura if the epidermis is still there. (See Rhynie Chert News 61, 91.)

It is not known whether the decay-resistant tube amidst the cortex makes Ventarura unique or is present in some other fossil or extant plant, too. The hollow straw aspect occasionally seen with Aglaophyton, well known but misinterpreted, is possibly brought about by essentially the same sequence of processes and hence can lead to an explanation of the conspicuous phenomenon in either plant.
(See Rhynie Chert News 83 .)
Judging from more than a dozen small chert samples with Ventarura found hitherto, this plant seems to be more widely distributed in the chert but had been overlooked. Hence, more finds are likely, which may help to answer the remaining questions raised by the peculiar features of this fossil.
The shoot cross-section seen here was enigmatic until the publication [1] on
Ventarura appeared in 2000. A cross-section with unique aspect is shown in Rhynie Chert News 96.
Considering that Ventarura and Trichopherophyton are the least abundant ones among the land plants in the Rhynie chert, the presence of the two zosterophylls in one chert sample must be a rare coincidence. (See Rhynie Chert News 95 .)

[1]  C.L. Powell, D. Edwards, N.H. Trewin: A new vascular plant from the Lower Devonian Windyfield chert, Rhynie,
      Trans. Roy. Soc. Edingurgh, Earth Sci. 90 (2000 for 1999), 331-349.

H.-J. Weiss       2012,     emended 2014, 2016.

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