I got the mother plant as a baby from a wild colony of exclusively single-flowered plants growing in a medieval ruin.
It grew up nicely and bloomed single as was to be expected.
The next spring I had some self-set seedlings in pots which i potted up and to my amazement, from the 5 offspring plants I had, 4 where double-bloomed looking like the cultivar Tanacetum parthenium 'Flore-pleno'.
I have never had the double-flowered form..
Maybe not a big deal, but anyhow it find it strange..
