I collected seeds of Astrophytum myriostigma cv Onzuka and sowed on 24/08/2008. I grafted several young seedlings.
Cv Onzuka was developped by Mr Onzuka, living in Okayama pref Japan.
He found a very white myriostigma in 1975 and fixed the gene by himself.
Cv Onzuka will be an elongated shape if it was grown own-root/seedlings.
If you want to make a flat Onzuka, you might graft seedling and degraft later.
This is a grafted Onzuka, flat shape, 9 cm diameter. I will degraft soon.