I have a theory about pearling.
Plants release oxygen during daytime, and the visible "pearling" bubbles seem to always appear after a good trim.
IMO, this is why everyone loves riccia for pearling--it does it on its own, but riccia inherently necessitates trimming because it grows so fast. Trim almost any plants, and the o2 will bubble out of the severed area like its bleeding oxygen. Again, I think plants always pearl, but pearl most once you have trimmed them (Anacharis is another perfect example of a good pearler)