Senecio jacobaea Brot. ex Willk. & Lange species
-> accepted, 149k occurrences
Senecio jacobaea L.
-> synonym of Jacobaea vulgaris Gaertn., 3,5k occurrences
Senecio jacobaea Kunze species
-> doubtful, 2,5k European occurrences, 2 child varieties
Senecio jacobaea D.Don species
-> doubtful, no occurrences
From Euro+Med & Tropicos it appears only the Linnean synonym is recognized
The Plant List does contain all those names above, treats the Linnean version as a synonym and has all others as "unresolved":
It seems correct that all those names are in the backbone, but as far as I have reviewed all occurrences come in as plain "Senecio jacobea" or "Senecio jacobea L." and should therefore not be attached to any of the non Linnean names. Examples:
The occurrences attached to S. jacobea Kunze appear to be linked to the 2 varieties:
Senecio jacobaea var. jacobaea
(verbatim=Senecio jacobaea subsp. jacobaea)
Jacobaea vulgaris subsp. gotlandica (Neuman) B.Nord.
(verbatim=Jacobaea vulgaris subsp. gotlandica)
So this is mostly an issue with occurrence name matching which has to be improved to deal with authorship and probably better consider ranks.
In order to allow the species matching to prefer matches to Linnee instead of the accepted Willk. & Lange name that name should also be doubtful and not accepted.
As improved species matching is handled in
POR-2768 this issue should focus on making Senecio jacobaea Brot. ex Willk. & Lange doubtful instead