Another new nematophyte in the Rhynie chert

A nematophyte which differs from the hitherto known ones has been discovered unexpectedly after repeated inspection of a Rhynie chert sample stored here since 2005. Despite of its poor state of preservation, a few characteristic details have been found.
nematophyte in chert
Fig.1: Nematophyte, largely decayed and replaced by quartz grains and voids inside, filamentous structure partially preserved in some places near the boundary. Width of the image 17mm.

With tube diameters ranging from well below 10Ám up to 27Ám and a width of the whole organism of hardly more than 2cm, this nematophyte seems to be comparable to the flat one shown in Rhynie Chert News 46 but it lacks the clearly structured outer sheath seen on that specimen. In the present state this nematophyte is bounded by an apparent envelope, which had partially been detached before silicification. This envelope might have been formed by dried-up organic gel, as suggested by the aspect of the better preserved nematophyte in Rhynie Chert News 98.
Things are slightly confusing since the organic gel between the filaments or tubes becomes replaced by silica gel, probably when the organic matter degrades and produces low pH as it is known from degrading plants.
This specimen does not consist of displaced fragments but had got into the swamp matter and remained there as a whole. (It is not seen here as a whole because it slightly extends beyond the edge of the chert sample seen on the left. 2cm-wide sections of the whole specimen are on the back of this 5mm slab and on the adjacent face of the next slab of 10mm, where the specimen ends inside.)
Several conclusions can be derived from the conspicuous former crack filled with white chalzedony. It seems out of place among cavities left by the decayed nematophyte weft. It indicates that there had been some solid state, mechanically homogeneous, probably silica gel from early silicification. (The organic gel, which is thought to keep the live filaments together and to keep the dirt out, would most probably not be so stiff that the weft could break.) Bending stress on the weft gave rise to a crack starting from the upper boundary and stopping at the lower boundary, which indicates that the swamp matter was still fluid. The silica-rich water in the crack turned into silica gel and later into white chalzedony. It remains an open question why the crack fill is still there while the surrounding silica gel either vanished or recrystallized into quartz.
A tolerably well preserved weft of tubes with characteristic features is only seen on the right in Fig.1. The following pictures, width 1.4mm, show details from there.
nematophyte tubes
Figs.2,3: Nematophyte tubes arranged not quite randomly: bundles of parallel or diverging tubes, pale spots between the tangle of tubes.

Similar as with other nematophytes the
tubes seem to be randomly arranged, with various deviations from randomness. Here, the orientation is governed by some local texture usually less conspicuous than the bunches in Fig.2. There can be "glades in the jungle", more or less clear spots of unknown origin and purpose, as seen in the lower halves of Figs.2,3. Their abundance can exceed one per square millimeter. A diverging bundle of tubes is seen on the right in Fig.3. (The irregular bright specks indicate areas of the nematophyte which had been decayed before silicification and hence are not relevant here.) A small part of the dark boundary is seen in Fig.3 below right.
nematophyte tubes
Fig.4: Nematophyte with narrow tubes near its boundary on the right, a pale spot (incidentally ?) extending from there and protruding into the surrounding chert with mineral debris.
Two of the pale "glades" differ from the others by their elongated shape and sparsely distributed narrow tubes of about 12Ám, with the bigger tubes keeping out. Their similar aspect seems to indicate that they are no incidental formations but their purpose is not obvious. Also seen in Fig.4 is an abundance of narrow tubes near an apparent boundary of the nematophyte (incidentally ?) bordering on the pale spot.

globules in decaying nematophyteFig.5: Unidentified globules in a place of decayed and vanished nematophyte tubes; degraded tubes on the left and below.

Globules like those in Fig.5, single or clustered, are seen scattered across the whole nematophyte section. They have got a tiny dark rod inside which often appears as a black dot on the surface. Judging from their deformation at mutual contact, they are of a soft consistence. Most probably they do not belong to the nematophyte but prefer growing inside it.
A large part of the weft of tubes in Fig.1, where not vanished at all, looks as degraded as seen in Fig.5. A few thin dark lines seem to be shrunken tube contents.
Any new find of a nematophyte, even if poorly preserved, can contribute to an understanding of these rare "enigmatic organisms" [1].

H.-J. Weiss        2016,     revised Dec.2016

[1] T.N. Taylor, E.L.Taylor, M. Krings: Paleobotany, Elsevier 2009.

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