Helianthus tuberosus and H. x laetiflorus
Often users take for granted that all perennial sunflowers are to be identified as Helianthus tuberosus. Actually many, if not most, observations depict Helianthus x laetiflorus.
Here some works on the two taxa:
https://www.biodiversitylibrary.org/item/14536#page/129/mode/1up
http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=114871
https://www.researchgate.net/profile/Lajos_Balogh4/publication/296815285_Sunflower_species_Helianthus_spp/links/56dabfbd08aee73df6d2ab23/Sunflower-species-Helianthus-spp.pdf
https://www.degruyter.com/downloadpdf/j/botlit.2014.20.issue-2/botlit-2014-0018/botlit-2014-0018.pdf
