Enigma inside Aglaophyton spores
deutsche Version

Aglaophyton sporangiumSpores of the early land plants of the Devonian Rhynie chert are found in their sporangia or scattered throughout. Aglaophyton spores are often seen in large numbers but germinating ones are very rare. Nevertheless they had been found and pictured in several stages of germination [1].
Those pictures do not provide any indication of structures inside the spores.
The present pictures show a distinct structure in one spore and less distinct ones in a few others. It looks like a small patch of tissue consisting of tiny unequal polyhedral cells and a few not yet finished cell walls protruding at edges. Apparently, Aglaophyton spores of such aspect had not been described before.
It is thinkable that an advanced stage of the phenomenon could provide the aspect of Dictyotriletes spores [1,2]. This would raise the question of the compatibility with Retusotriletes spores [1], which are usually associated with Aglaophyton.
Independent of possible affiliations there is the relevant problem of whether the structure seen inside the spore is an hitherto unnoticed early stage of germination or something else.
A search for more spores with inner structure among the Rhynie chert samples stored in collections might help to answer the remaining questions.

Figs.1,2:  Aglaophyton sporangium,
detail with palisade wall and variously affected spores, a few ones with distinct structure inside. Spore size up to 70Ám. Width of the pictures 1.4mm.
Sample: Rh2_8 (1.36kg), Part 1, obtained from Shanks in 2000.

Aglaophyton sporangium
H.-J. Weiss       2020

[1] www.abdn.ac.uk/rhynie/spores.htm
[2]  C. Rubinstein, J.H.G. Melob, Ph. Steemans: Lochkovian (earliest Devonian) miospores ... Rev. Palaeobot. Palyn. 133 (Jan 2005), 91-113.
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