The sporangia most easily recognized as such in the Rhynie chert are those of Aglaophyton. They are often split lengthwise (Fig.1), and they sometimes show a distinct twist in the texture of the wall. This led to the assumption that the twist might have originated as a result of splitting [1], as it is known from the seed pods of several leguminous plants, where mechanical stress built up during maturing is released in a sudden burst scattering the seeds and leaving the halves of the empty pod in a twisted state.

There is, however, ample evidence that the twist of Aglaophyton sporangia is not due to splitting but is an inherent feature. Fig.2 provides a view on the outside of a sporangium lying just below the cut and polished face of the chert sample. Apparently the sporangium is not split but the twist in the texture of the outer wall is clearly there. More evidence comes from inclined sections of non-split sporangia (Fig.3): The sporangium wall cells appear wider on one side of the capsule and narrower on the opposite side. This is what is expected from elongated cells arranged nearly parallel to the axis of the lengthy capsule except for a slight twist or spiral texture, since they are more inclined with respect to the cut face on one side and less inclined on the other one so that their width seems to vary along the circumference.

						Fig.1: Cross section of empty Aglaophyton sporangium.
						Fig.2: Side view on Aglaophyton sporangium.
						Fig.3: Inclined section of non-split Aglaophyton sporangium.

In [1], an epidermis texture is shown which seems to belong to a sporangium with a left-handed twist, while ours in Fig.2 is clearly right-handed. This is suspicious since Nature often prefers one type of thread. For example, the fruiting bodies of the stoneworts (Characeae), called gyrogonites, have come with a left-hand thread through the ages up to present. The suspicion gives rise to the following idea: The picture in [1] had been obtained with the peel technique which provides the mirror image of the real thing and hence transforms right into left if one does not take care to reverse it before printing. (This probably also applies to pictures of right-handed gyrogonites occasionally seen in the literature.)

In this connection it is interesting to compare the handedness of other twisted sporangia as they are known from a few more early fossil land plants (Rhynia, Huvenia, Torticaulis) and extant mosses. Sporangia of one species with either handedness are shown in [2] without any comment on the difference. Apparently the type of thread is not always conserved in the reproduction of pictures in botany but no-one seems to bother. In view of this state of things it would be interesting to find out whether the thread of twisted sporangia is equal among related species so that it could serve as a useful feature in cladistics.

Text: H.-J. WEISS/Rabenau, Fotographs: H. SAHM/Dresden