could also be a seedling of li parentage.
li is not as thorny as rootstoc, but li's thorns may grow as long as the rootstocks', and generally thicker. Speaking of rootstock and seedlings, there are at least three thorny rootstock cultivars we've identified, that we couldn't anymore identify which might be the true wild-type spinosa. And judging from one of the late Roger Meyer's specimens, he seemed to have used another rootstoc cultivar, which continue to crowd the growing number of impostors.
the cultivar jin is another rootstock impostor, and could just surmise it was grown from a rootstoc seedling.
incidentally, if the herbaceous leaf-bearing stems(deciduous fruiting/flowering stems) have tiny leaves and are thorny, then it likely has strong rootstock genes. Most domesticated cultivars' deciduous fruiting stems don't have thorns.
to complicate matters, li may exhibit this thorny trait on some of its fruiting stems, but none on other fruiting stems--on the same tree.
btw, @thecityman and @k8tpayaso 's froggies seem to be competing for a cuteness award. Somewhat worried about any of them accidentally landing on and getting impaled by a 1.5 " thorn, yikes!