hmm. I have tried a few times to propagate via root cuttings and zero… true Illini doesnt sucker as far as i can tell. Primocanes come from the crown only as far as i can tell also. Its very very erect so the only way to get a ‘patch’ would be those low laterals somehow tip rooting…i just dont see it tip rooting any other way.
Perhaps its ‘Ebony King’ which is very close looking and also very thorny…it suckers like crazy and a ‘patch’ would be easy. Or perhaps someone down the line grew out seeds and called it Illini? Hard to know.
There was a thread years ago about Illini being ‘invasive’… i just dont see that being possible with a true to name Illini. Its one of the most well behaved plants that i have seen other than being thorny.