Jan, I think it actually may be, a better representation, of what's more commonly grown, in the way of Iris, determined mainly by "Search Results', of what member's here , grow, when it is by 'Relevance'. That could possibly be why, there is a difference in the lists, (for the first page) of each "results" listed, between 'Popularity" & "Relevance"... Although, it may also quite possibly show, what is more easily, widely grown & may multiply, or tend to "increase", in most areas of the U.S. ( mainly.)
Personally, I thought there are many more "white" Iris, which are better looking, than 'Immortality'. Although, I'm fairly sure, it was "promoted" quite a bit more, due to being a "re-blooming" Iris.
While I have no idea, how a certain cultivar "name" such as 'Immortality', may actually play any role or part, with it's "Popularity." Although, I tend to think, it may have actually had an effect, with 'Stairway To Heaven' !
But apparently , there were several more Iris listed ahead of 'Immortality", by way of the "General Search" results, if you have look again, & notice...No idea, what effects, any "Artificial Intelligence' may play, in any of the search results ! It seems to quite often be used rather typically, these days...
