If I remember correctly, there was this hypothesis that these things were covered by symbiotic algae so the idea is that they grew tall to increase the photosyn

If I remember correctly, there was this hypothesis that these things were covered by symbiotic algae so the idea is that they grew tall to increase the photosynthesis of their symbiotic organism (so kind of a giant lichen). But I can't find the source anymore, and I think that there isn't much evidence of any photobiont.