Hi, welcome to GoY, I have never heard of a white mellar plant, but there iw a plant with the common name white madar, google Calotropis gigantea, it isn't hardy in the uk, and would need taking inside for the winter, Derek.

I thought it said white medlar. and if it is then it becomes a large tree in time.

Do you know its correct botanical name? It will help give you the best advice.

Can you ask the person who gave you the seeds what sort of plant it is?