We do not currently know of any antonyms for swallowwort.
The noun swallowwort is defined as:
Any of several vines of genus Vincetoxicum (syn Cynanchum), especially black swallowwort (Vincetoxicum nigrum, syn. Cynanchum nigrum) or white swallowwort (Vincetoxicum hirundinaria, syn. Cynanchum vincetoxicum)