No, not all Cladophora is epiphytic, this one actually is not epiphytioc at all, it gets entangled, but I've never found it truly attached to a plant.
If you are killing it with blackouts, It's not this alga, it's likely Vaucheria or Rhizoclonium.
There are a few algae that look close to this one.
If it's only in the Riccia, Heck toss the Riccia and pick off a tiny piece to re grow the Riccia without it.
Harassment works also, removal of the plants that allow it to stay entangled will help.
It will attach to gravel and sometimes wood etc and likes flowing water, if it's unbranched and soft, it's often Rhizoclonium, if tough and unbranched, often Dicotomosiphon. Vaucheria needs an iodine test for starch negative.
There are others.
I've seen it go away in tanks not come back on several ocassions so there seems to be some trigger.
Aggressive attacks will help. Also, I've let other plants over shade and out grow it and then it's died back, this worked well with pearl grass.
It's more like a higher plant in many respects, it's large, thick walled, Chl a and B, starch reserves etc. Not too tasty either.
I had 50 Shrimp in a 40 gal. Took them two weeks but admittedly the tank was taken care of better but no algae removal was performed also.