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
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All this are good. But how to distinguish the wild forms of Helianthus tuberosus from H. x laetiflorus? Is it possible? I observed H. tuberosus become "H. x laetiflorus" in a few years in an abandoned garden on poor sandy soils . The size of the heads, the shape of the leaves and even the pubescence are changed.
Your comment is really interesting.
Here in Tuscany most plants are compatible with H. x laetiflorus but few still seem to conserve the characters of H. tuberosus thus I thought that the phenomenon you described could not occur. Moreover they are mostly sterile so pollen transfer seems to be unuseful for fruit set and characters mixing seems unlikely.
I don't mind. In Central Russia, sunflower thickets are grow near suburban housing, summer cottages, and so on. Over time, the size of the tubers decreases, the leaves become narrower. This is especially fast on poor soils. I do not believe in the conversion of species, of course. But I do not have exact vouchers of H. x laetiflorus.
Every time I see sunflowers, I remember these problems.
Also the decrease in size of tubers is always observed in the Italian presumed H. laetiflorus.
Your comment suggests to get more insight into this issue and that the implementation of a research at the European level with the involvement of researchers skilled in plant genetics could be interesting.
Anyway, just in order to highligh that many observed plants corresponf to the "concept" of H. x laetiflorus, I would go on indentifying plants following the aforementioned references.
Hi blue, thank you also for this card.
Marco
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