Aglaophyton spores decayed inside sporangia
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Aglaophyton sporangium 7mmAglaophyton, the most abundant of the early land plants preserved in the silicified Early Devonian habitat known as Rhynie chert, still offers interesting details which occasionally even contradict views established in the scientific literature. The maximum diameter of its fusiform sporangia is 4-5mm according to [1], 4mm according to [2], but 6.5mm in Rhynie Chert News 11, about 7mm in Rhynie Chert News 61, and 7mm in Fig.1.
The twisted sporangia had led to the idea that the twist came with the splitting [1], which has been refuted. These references show that it is still worthwhile to closely look at Aglaophyton.

Fig.1: Big Aglaophyton sporangium, diameter 7mm, filled with damaged spores,
            bluish chalcedony, and coarse crystalline quartz.

The sporangium seen here is highly peculiar for more than one reason. Its diameter of 7mm is among the biggest ever seen. It is not obvious why a well-defined curved boundary had separated the mass of spores below from a water-filled cavity above. The cavity walls and a few fungus hyphae grown in the silica-rich water (on the left) had become coated with silica gel turning into bluish chalcedony. Later the remaining cavity became filled with coarse crystalline quartz.
Most remarkable is the uncommon aspect of the spores, not chewed up by spore eaters but severely damaged nevertheless (Figs.2,3). These detail images are representative for the heap of spores in Fig.1. Since essentially all spores seem to be affected by the same type of damage, one may wonder whether decay due to being submersed for a long time before silicification or a quite different phenomenon had been at work. This
small chert sample (15g) does not offer another big sporangium for comparison but a smaller sporangium (Fig.4) provides additional insights.
Aglaophyton sporangium, damaged sporesAglaophyton spores, damaged
Figs.2,3: Damaged Aglaophyton spores inside the sporangium of Fig.1. Image widths 2mm, 1.2mm.

Fig.4 suggests the idea of some destructive process encroaching on the nearly globular spores or tetrads, mostly pale and a few black as seen above left. (The black ones seem to be coated with a microbial layer.) Below left, only a few spores are seen affected, apparently with holes in the wall. Quite different is the aspect on the right where the destructive process had reduced the spores to debris.

Aglaophyton spores, partially damaged

Fig.4 (right):
Aglaophyton spores, well preserved or damaged, inside a smaller sporangium,
         same sample as Fig.1. Image width 1.1mm.

Fig.5: Detail of an Aglaophyton sporangium in Rhynie Chert News 166 with an enigmatic structure
        clearly seen inside a transparent spore. Image width 1.1mm, same scale of Figs.3-5.
Aglaophyton spores

No explanation is proposed here for the destruction of spores inside sporangia. A related observation (Fig.5), where a transparent spore is seen with a definite enigmatic structure inside, can possibly lead the way to an explanation. Nearby spores, too, are structured inside but less clearly seen.
Sample: Rh4/67 (15g) found in 2009.

H.-J. Weiss 2021

[1] D.S. Edwards : Aglaophyton major, a non-vascular land-plant from the Devonian Rhynie Chert.
     Bot. J. Linn. Soc. 93(1986), 173-204.

[2] Aglaophyton
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