Symbiotic fungus in Trichopherophyton
with dark fill, loosely arranged in a concentric cylindrical area in
the shoot of a plant and seen on cross-sections
as a dark ring at some distance below the
epidermis is a common sight in the Lower Devonian Rhynie chert. Most
cross-sections with dark ring are Aglaophyton
(former Rhynia major).
Quite similar rings on cross-sections of the smaller Rhynia
are not rare. The phenomenon has been
described in detail and explained as being due to the fungus Glomites rhyniensis
engaged in a type of symbiosis known as
arbuscular mycorrhiza . It would
be interesting to know, of course, whether or not such symbiosis had
been more widespread among the Lower Devonian plant species.
Evidence is provided here of the occasional
occurrence of quite
similar arrangements of cells with dark fill in the "hair-bearing
which is not related to Aglaophyton.
one of the less abundant plants in the chert, and it is easily
recognized only if the less often preserved upper parts with the
bristles are seen, as in these pictures. (The
big bristle below left in Fig.1, length 1.55mm, might be one of the
longest ever seen on this plant. With superficial inspection it could
be mistaken for a crack.)
Fig.1 (left): Three bristly
cross-sections of Trichopherophyton in
full view and about five more partially seen on this small
area of 7mm width. Note also the big bristle below left.
Figs.2,3: Cells with dark fill loosely arranged as a dark ring on Trichopherophyton
Width of the pictures 4mm. Same scale for Figs.1-3.
Fig.4: Detail of Fig.3. Cells with dark stain and definite
contrasting to the degraded tissue around.
Width of the picture 1.3mm.
the plant parts with dark cells as those in Figs.2,3 and others had not
been less vigorous than those without. Thus one may conclude that
the dark fill did not do any harm and perhaps had even been beneficial
as previously assumed in connection with Aglaophyton .
As seen in Fig.4, the dark stain is confined to individual cells which are in a better state of preservation than the largely decayed tissue
harbouring them. (The
hyphae vaguely seen in Fig.4 as thin dark lines could as well belong to
some rot fungus also present in this chert sample.)
What needs to be done with higher resolution is to show that
the dark fill
consists of fungus arbuscules. This would be another piece of evidence of this type of symbiosis between fungi
 T.N. Taylor
et al.: Fossil arbuscular mycorrhizae from the Early
Mycologia 87(1995), 560-73.