If you need to find the type of vegetation, you may go for isotopic analysis that can easily distinguish different types.

Also you can see the papers of Dr Seema Singh: https://www.researchgate.net/profile/Seema_Singh27

Hello,

I think that only base on the morphology of the rhizolith, or tuffa it is impossible.

You need to find some seeds, or real organic material.

Dear Dr. Singh;

Thank you very much for your contribution and the attached paper. I will try oxygen isotope analysis.

Dear Dr Juilleret;

Thank you very much for your advise. I will try to extract some pollen grains, if any,  in my samples. Little preserved morphology of plant tissue my be useful?. Please check the attached photo.