Great question Mark. There is the possibility that if there are some prickles (moss) the concentration can increase. However, if there really isn’t any signs of moss I highly doubt if it will become mossy. DeVries and colleagues looked at the inheritance of moss from the old moss roses and published a paper on it in 1984 (Gartenbauwissenschaft 49(3):97-100). They looked at the inheritance of recurrent flowering as well in these populations. Moss fit a single dominant gene model. What I can recall from my experience with ‘Scarlet Moss’ it seemed like ~half of the seedlings with non-mossed parents were mossed. THis would lead us to suspect the genotype of ‘SM’ is Mmmm (assuming it is tetraploid). Half the time the sex cell will have Mm and contribute moss and the other half it will be mm and won’t. I believe there is one major gene controlling if there will be moss or not, but in the presence of the dominant allele allowing for moss then other more minor genes can contribute to the degree of mossing we observe.
Sincerely,
David