Trichopherophyton and Ventarura in one chert sample
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Trichopherophyton beside Ventarura
The mere fact that the two rarest and therefore last discovered plants [1,2] in the Lower Devonian Rhynie chert have been found together in one piece of chert seems worth mentioning. 

Fig.1 (right): Cross-sections of more or less deformed shoots of Ventarura and smaller Trichopherophyton with bristles. Width of the image 17mm.

Fig.2 (below):
Cross-section of well-preserved Trichopherophyton beside lengthwise section of Ventarura. Width of the image 8mm.

Trichopherophyton beside Ventarura

Trichopherophyton is easily recognized here by its bristles but often it is seen without. (See Rhynie Chert News 49, Fig.3.) Then it may be distinguished from Rhynia, whose diameter is in the same range, by the scalariform pattern on the tracheid walls seen on longitudinal cuts of the xylem strand.  Apparently the bristles served as a protection of the sporangia against spore-eating crawling creatures. This is suggested by the fact that the bristles are borne only on the upper parts of the plant. No other species in this Lower Devonian habitat had developed such protection. Unlike other plants in the chert, Trichopherophyton is often seen in good shape and with well-preserved tissue, as in Fig.2.
Ventarura is the bigger one, as seen in Fig.1 above right and in Fig.2 below left. Its upper parts are distinguished by a unique feature of a quite different kind: It is a big tube of rot-resistant tissue appearing on cross-sections as a ring with clearly visible cell structure, most often with dark aspect, which gives the impression of strength and has misled some observers to an interpretation as sclerenchyma. Such interpretation has been rejected by the observation that the cell walls are normally thin but appear thick owing to a dark
coating, probably of microbial origin and grown while the dead plant was decaying in the swamp water. (See Rhynie Chert News 60, Fig.6.) Occasionally the tube is the only part of Ventarura that is seen, as in the case of the lengthwise section in Fig.2. Apart from its conspicuous appearance in the chert, the persistent tube must have had a purpose in the live plant. A purpose, however, is not obvious. With its position inside the cortex tissue it would not have protected against damage to the surface. As a far-fetched interpretation, the tube, if poisonous or tasting bad, could have prevented sap-sucking creatures from gnawing towards the phloem surrounding the xylem strand.
The two rare plants were first seen together in one sample in 2014.

H.-J. Weiss     2016

[1]   A.G. Lyon, D. Edwards: The first Zosterophyll from the Lower Devonian Rhynie Chert.
      Trans. Roy. Soc. Edinburgh, Earth Sci. 82(1991), 323.
[2]  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.

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