A Devonian alga with peculiar features (Part 3)
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When the unknown alga first described under this headline was found in another Rhynie chert sample, then described in Part 2, the suspicion arose that it is not extremely rare but, when there, nearly always overlooked. This immediately raised the question why this intriguing fossil could have been overlooked. Now a small chert sample of 30g can provide a possible answer.
(By the way, a curious but irrelevant coincidence may be mentioned here: The sample had been found one day before the Rhynie Chert Conference 2003, where detailed work [1] on Palaeonitella was presented. The sample was registered and shelved as of no major interest until it became highly interesting by another investigation a few days ago, at the end of 2015.)  
With the recently discovered "alga flowers" in mind, one can see relevant details not seen before on the surface of this sample. The sterile parts are liable to be taken for Palaeonitella [1], and the fertile parts are rather rare, and when present, not well preserved so that the enigmatic capsules are easily mistaken for the ubiqitous globular fungus organs scattered among plant matter in the chert. 
alga top with capsules, Rhyniealga top RhynieThe dark objects in Fig.1, for example, are likely to be mistaken for randomly distributed chlamydospores but they are not mutually unrelated, which becomes apparent by thorough inspection only. The yellow stick below one of the objects gives a clue. One can guess that a faint streak attached to the other object is another stick or stalk. The two of them point to a common centre. If there is a centre, it can be an aid to see more: Another yellow stalk connects the centre with a yellow object similar to the dark ones, dimly seen in the depth. A bright yellow dot is the cross-section of a stalk pointing towards the observer. Mere pale shadows are left of another two rounded objects below right.

Figs.1,2: Two capsules whose mutual correlation reveals their nature as parts of an "alga flower". Width of all pictures 1mm.

After it has become obvious from Fig.1 that there is a "flowering alga" in the sample, it is less difficult to see more "flowers" even if they do not stand out clearly among the numerous sections of alga branches of various orientation. Enhanced contrast and sharpened outlines did not much contribute to the visibility of the relevant details in Figs.3,4. A decaying enclosure with 5 or 6 capsules inside, one of them with sharp outline, can be discerned in Fig.3. The outline is faded on the 8 or more capsules in Fig.4. It is not known whether
the vanishing capsule wall and the dots inside are something essential in the life cycle or merely the result of general decay.alga top Rhynie
alga top Rhynie
Fig.3: "Alga flower" with capsules likely to be mistaken for branch sections, surrounded by curved branches in a state of partial decay.

"Alga flower" with poorly preserved capsules arranged around a very faintly seen columella, all in a basket made of curved branches.

With superficial inspection the elliptical spots in Fig.4 with black dots inside might not be recognized as something special but one detail provides the proof that what is seen in Fig.4 is an "alga flower": 
In order to locate it in this confusing picture, one may start from the elliptical spot above right. A long slender stalk, very faintly seen, extends from there towards below left, crossing the dark spot in the background and ending above the pale yellow spot, where it meets 4 stalks from other directions at a common point. Only very short parts are seen of the latter stalks so that the centre looks like a small non-conspicuous "star". It is the tip of the columella where the stalks are attached.
To sum up, the above figures have confirmed the suspicion that the peculiar alga details can easily be overlooked for various reasons. As a disturbing fact,  thorough inspection does not seem to have removed the problems and discrepancies with the fossil charophyte algae preserved in the Rhynie chert. 

Apparently the "alga flowers" described in the present contributions have not been described elsewhere.
(2) The "alga flowers" are formed as a basket or cup made of branches which can be either wound (present sample, Fig.4)
      or only curved inward 
(Rhynie Chert News 73).

(3) Sterile whorls with spirally wound branches in the present sample (Fig.5) resemble similar structures assigned to Palaeonitella in Rhynie Chert News 10.  
     They do not appear in the reconstruction of
Palaeonitella in [1].
(4) If the capsules on stalks seen in the
"alga flowers" turn out to be oogonia, the alga described here differs much from Palaeonitella in [1]
      and from any other charophyte alga with their gyrogonites.

alga basket Rhynie
Fig.5: Basket made of wound alga branches, seen from below. Width of the picture 1mm.

It is hoped that the search for more of the seemingly incompatible details of Devonian charophyte algae will finally lead to a consistent view.
Sample found in 2003, fossil seen in 2015.

Addendum: After correcting the scale in [2], Fig.3.56, by a factor of 10 or more, it becomes apparent that the danger of mistaking alga capsules for fungus chlamydospores is not only due to the similarity of shapes and sizes. The clusters of alga capsules with stalks might be mistaken for
Sclerocystis chlamydospores on hypha ends. 

H.-J. Weiss       2016

[1]  R. Kelman, M. Feist, N.H. Trewin, H. Hass : Charophyte algae from the Rhynie chert,
    Trans. Roy. Soc. Edinburgh, Earth Sciences 94(2004 for 2003), 445-455.
[2]  T.N.
Taylor et al.: Paleobotany (2009).

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