Question Author
Thank you both very much. Just the sort of answers I was hoping for. Just enough to help but not so much that it actually answered the question. I have spent another while to find the answer and had detours around purgatives and eliminating the buckthorn from various parts of the USA; also discovering the various kinds of Buckthorn. All added to my rather slim knowledge of the subject. Then I was nearly caught unawares by the english spelling when I finally hit upon the right answer. But I got there! Thank you so much
SJ