Peculiar charophyte alga in the Rhynie chert
deutsche Version

Charophyte algae are a common but enigmatic component of the Lower Devonian vegetation preserved in the Rhynie chert. They have been thought to largely belong to only one species named Palaeonitella, with gyrogonites for propagation like with any known
stonewort-like charophyte alga. While gyrogonites are readily found from the Devonian to the present so that they serve as index fossils for stratigraphy, those of  Palaeonitella had been elusive for decades. Their assumed discovery had been announced by the authors [1] with due caution because they had been found broken and detached from the alga so that their affiliation is not quite certain.
Recent own finds suggest that some or even all
stonewort-like charophyte alga in the Rhynie chert may represent a highly peculiar charophyte alga distinguished by the absence of gyrogonites. Arguments in favour of this idea have been offered in Rhynie Chert News 73, 89, 90, 138. The images shown there can be helpful in the interpretation of the often confusing images of poorly preserved or unfavourably cut algae. The present contribution is meant to complement the previous ones by providing more images, thus promoting the idea that this alga is a relic from bygone times when there were no gyrogonites.
peculiar alga toppeculiar charophyte toppeculiar charophyte alga top

Peculiar charophyte alga, uppermost whorl with oogonia, top viewPeculiar charophyte alga, uppermost whorl with oogonia, top viewPeculiar charophyte alga, uppermost whorl with oogonia, top view
Figs.1-6: Stonewort-like charophyte alga, 6 specimens, each with cross-section of uppermost whorl with multiple smooth-walled oogonia, top view.
Height of images 1mm.

On this alga, oogonia are grown at the uppermost whorl only, where they form a kind of "alga flower", not often as conspicuous as in
Rhynie Chert News 73, there Fig.1. Often the alga parts are arranged less orderly, owing to partial decay or inclined cut. Among the above images, only Fig.2 comes close to a "flower". It is not known why some oogonia have got a dark fill while others are transparent.
Even if poorly preserved, capsules and branches can be told apart by their diameters: 0.1 ... 0.13mm for capules, 0.15 ... 0.2mm for branches. The smaller branches in Fig.5 do not seem to belong to the decayed flower. 
Fig.5 is remarkable for the central column below right of the dark oogonium, with a few stalks of the shed oogonia still there. Two more oogonia with very pale stalks are faintly seen below.
The antheridia in this sample are like those in
Rhynie Chert News 93.
All pictures have been taken from the sample Rh9/93 found by S. Weiss in 2011. The "peculiar alga" had been discovered in 2015. 

H.-J. Weiss   2019

[1] 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.
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