I don’t know the details of this particular species, but I think you’re mostly seeing differences in citation format. Plant names with authors are meant to be like literature citations, to help guide you to the original species description, but it can get complicated. In this case, Weihe described the species, but maybe in a book written by other people. So, maybe some resources cite only Weihe for the species, but others also note the authors of the flora or whatever. I’m not sure about the Weihe & Nees here, but in some cases, maybe the author who described the species contributed the description to a treatment that was known be written by someone else. (For example, maybe Nees wrote a treatment of Rubus for a book, mentions “my pal George found this new species and I’m including his description here” and then the whole treatment goes into a flora that was mostly written/edited by other people.) So, deciding on the best approach to cite all the people responsible for getting the new name published becomes complex, and different databases and workers will use different formats. Some only care about the main author of the species, but others like all of the information included.
IPNI was digitized from a book published in 1894, before there was a botanical code. Today we follow the 2025 Madrid code which has very specific rules on how an author must be cited.
In POWO all those old IPNI records have been checked with current literature and following the current rules, so that should be most up-to-date.
Since IPNI was digitized in 1971 much of the data has been standardized but only corrected based on contributors comments and feedback.
duplicates in IPNI should be ignored, there are merely there for historic reasons (as IPNI was the bringing together of 4 databases). They are never edited nor standardized.
Agreed. Many species descriptions from the 1800s have somewhat ambiguous sources in terms of how the author is cited, and if it’s a publication within a bigger publication such as a multi-authored survey report. And different modern researchers reference the source and its citation in different ways. I’ve seen this in vertebrate author citations.