In view of the fact that no living plant can be regarded as a close relative of one of the 7 "higher" terrestrial plants discovered so far in the Rhynie cherts, it is surprising that the green alga Palaeonitella looks rather similar to extant Nitella, a water weed of the stonewort clade, indicating that evolution was very slow in this branch of charophyte alga for 400 million years at least. Palaeonitella cranii was first described in 1921 [1] without the characteristic fruiting bodies (oogonia), which are called gyrogonites because of their twisted appearance. The gyrogonites of Palaeonitella were discovered only recently, which gave rise to a re-evaluation of the species [2].

In this connection it is vexing to have got a chert sample with abundant Palaeonitella, as it seems (Fig.1), and spiralling structures (Fig.2 & Fig.3) which superficially resemble gyrogonites but are much larger than those reported in [2], see Fig.4. They are made up of spiralling cells wound around a globular space or body of uncertain nature. (It must be mentioned that the stem segments, spiral members, and most branches consist of only one big tube-like cell, just like extant Nitella.) In Fig.2, the spiral members fit closely together on the left and above, the apparent gaps being due to the fact that in some places only the formerly hollow and later filled interior of the tube-like cells is seen in optical contrast, but there are real gaps between the cells on the right. The number of spiralling cells in these objects seems to be 5 or 6 (or more ?). Judging from the sparse evidence obtained from this chert sample, the set of 5 or 6 intertwined odd-shaped spirals does not have 5- or 6-fold symmetry but is strangely lopsided, as indicated by these pictures, and does not form a closed space.

						Fig.1: Upper whorls of Palaeonitella, silicified while standing upright in the water.
						Fig.2: View into a spiral object seen in clear chalcedony.
						Fig.3: Spiral object seen on a cut but not polished chert face.
						Fig.4: Drawings of several spiral objects.

As these objects are of about the same size as the antheridia described in [2], they could possibly be cup-like enclosures for antheridia, a feature apparently not observed before. Can P. cranii be so variable as to bring forth such uncommon forms or is it a new species ? In view of the current opinion that “there is no evidence of the presence of more than one species of charophyte in the Rhynie chert” [2], p 451, this would be interesting news. Anyway, the spiral structures visualize how the gyrogonites could have evolved from spiralling whorls of branches: In the course of evolution, the whorls protecting the oogonia apparently contracted into tightly fitting capsules while those wound around the antheridia preserved an ancient state of partial cover.

text, photographs & drawings: H.-J. WEISS/Rabenau, photograph: H.SAHM/Dresden