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Discussion Starter · #1 ·
help needed! i suspect of having two different species of riccia in my tank: riccia fluitans and riccia something-else. my guess is that this other one is riccia rhenana - it is dark green, does not peral as readily as r. fluitans, and it doesn't float but readily sinks to the bottom and spreads profusely. attached are photos, any imput welcome. this matter already caused some serious discussion on local forum, but unfortunately with no positive identification.

thanks!



 

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I can't give you a firm ID, nor can I positively state that you've got two species there, but I know that the USDA has descriptions of 33 species of Riccia and all can be found world-wide. I would imagine that many could be found together and thereby be collected together and sold as the same species.

If I had those and 'one' seemed to grow faster and stay submerged without all the tying-down of the 'other', I'd smile a big smile and keep the 'one' and toss the 'other'. :D

-Dave

ps. sorry I couldn't help with a positive ID.
 

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Riccia fluitans sometimes converts to a darker green sinking form and that's what you have. There are several varieties of the species and some are more prone to it than others. I'm not sure anybody really knows what makes it convert, but it may be a sort of 'overwintering' mode. Same species, different growth form.
 

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Discussion Starter · #5 ·
@cavan allen: I don't think this is the case here. As you said, R. fluitans may change its form when preparing for hibernation. That would mean that in my tank one part of R. fluitans is constantly preparing for hibernation, whereas one part continues to thrive in its usual form. This makes no sense. Both Riccias grow in one tank under exactly the same conditions, one next to the other. There is no trigger that could cause changes in plant’s physiology. Alternatively, I would expect that the hibernating form eventually returns to its "original" form, but this never happens, which further proves my idea that those are two different species...

if for somereason both are r. fluitans, i would also like to know what may have caused changes in behaviour of one part of the population.
 

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You could try sending this to a university with lots of plant biologists. Southern Illinios University has a few on staff with a bryologist as well. I recently sent a moss photo to them for ID, but they haven't gotten back to me. :(

Anyway, lots of plants, aquatic or terrestrial, can change forms for unknown reasons. I was collecting Black-Eyed Susan seeds last year for a USDA study and noticed something similar. I found two growth forms of the same species in a localized area, same soil, same moisture, sun exposure...but one group was tall, full of seeds, and very hirsutus compared to its counter-part just a few yards away (which was more bush-like, had more blooms, but far fewer seeds and less 'fuzzy').
Same species, but very different growth forms.

I'm not saying this is definitely the case for your Riccia, but it is certainly possible for both of those forms to be one species in the same.
 

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The hibernation theory was just a guess and basically ancillary to the main point; it is the same plant. Of that there is no doubt. Exactly what makes it change form is almost beside the point.

Sometimes the sinking form does revert back to the floating form. In the Baensch atlases, there is an entry for Riccia rehana, which is darker green and sinks. It was treated as another species before everyone realized it was just the sinking form of R. fluitans.
 
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