Charophyte lacking gyrogonites --- Palaeonitella centenary
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A fossil alga from the Lower Devonian Rhynie chert was named Palaeonitella cranii in 1921 [1] for its resemblance to the extant charophyte alga Nitella.
It had been thought to grow gyrogonites for propagation like any stonewort-like charophyte alga but "no specimens of the characteristic reproductive organs of the Characeae has as yet been found in the Rhynie deposit" [1]. 
Decades later, a few objects with spiralling aspect allegedly representing the elusive gyrogonites were found, hovever scattered and poorly preserved [2]. They were used for an emended diagnosis of Palaeonitella, including a fanciful reconstruction [2]. Devonian alga top
The elusive gyrogonites at Rhynie and the own finds of algae there provide quite another view, surprising as it seems: Most or even all stonewort-like charophyte algae in the Rhynie chert would never have grown gyrogonites but organs preceding them in evolution: oogonia without screw-like coating, nicely arranged at the top of the alga like stamina on a flower (Fig.1, more related pictures at [3]). Charophytes with simple oogonia are highly peculiar because they must be relics from bygone times when gyrogonites had not yet evolved. 
The question arises why the smooth oogonia have escaped the palaeobotanists' notice for a hundred years, although they are clearly seen on some own samples. (A related short paper sent to Paläontologische Zeitschrift in 2019 had been rejected.) As a possible answer, they are seldom as conspicuous as in Fig.1. Most often they are less clearly seen and likely to be mistaken for chlamydospores of unidentified fungi, as in Fig.2.
Incidentally the only objects which can doubtless be identified as oogonia in Fig.2 are those with obscure black and white fills. The transparent spheres in the foreground visualize the difficulty of telling smooth oogonia apart from fungus globules.

Devonian alga top
Fig.1 (above): Cross-section of a charophyte alga top end in Rhynie chert with an inner circle of ellipsoid- or bean-shaped smooth oogonia, mostly with dark fill, on slender stalks (not seen here), surrounded by cross-sections of the upright branches of the uppermost whorl. Image 1mm.

Fig.2: Lateral view of a slightly deranged charophyte alga top end in Rhynie chert with a few oogonia and branches of the uppermost whorl, with different orientation to the cut plane. Image 1mm.

The vain search for gyrogonites has not been useless because it has led to the assumption that Palaeonitella cranii [1] might represent the same species as the lately discovered charophyte alga with smooth oogonia, which would explain the lack of gyrogonites. This would imply that Palaeonitella cranii is not just another one among the many known charophyte algae but is an ancient species which had not taken the evolutionary step from simple oogonia to gyrogonites. Hence, its place on the phylogenic tree must be on a branch coming up from deep Silurian, well separated from the lot of the others. Apparently this particular branch ended soon since charophytes with simple oogonia without patterned coating have not been found in geological formations younger than Devonian.
In addition to this unexpected result, a less important thought may be mentioned: The genus name Palaeonitella, according to present knowledge denoting an ancient species lacking gyrogonites, should not be applied to fossils of advanced charophytes resembling Nitella, as done in 2021 [4].               
Samples: Fig.1: Rh10/42.2 (2013),    Fig.2: Rh9/86.2 (2003)

H.-J. Weiss        Dec. 2021

[1]   R. Kidston, W.H. Lang: On Old Red Sandstone plants showing structure ... Part V
       Trans. Roy. Soc. Edinburgh 52 (1921), 855-902.
[2]   R.Kelman, M. Feist, N.H. Trewin, H. Hass: Charophyte algae from the Rhynie chert.
       Trans. Roy. Soc. Edinburgh 94 Part 4 (2004 for 2003), 445-455.
[3]   H.-J. Weiss: Google: Chertnews: Rhynie Chert News 73, 89, 90, 138, 139.
[4]   C. Martin-Closas et. al.:
Palaeonitella trifurcata, a cortoid-building charophyte ...
        Rev. Pal. Pal. 295 (Dez.2021), 104523

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