In message , Kay
writes
In article , Stewart Robert Hinsley
writes

A round flower on a foxglove is called a peloric flower. This is not
the same as fasciation.

What causes it?

It's a mutation - hence the ability to purchase seed of peloric strains
of foxgloves.

I don't know the details, but I believe it's a mutation in a floral
development gene. Googling finds a statement that the peloric phenotype
in Antirrhinum is caused by loss of function mutations in the CYCLOIDEA
and DICHOTOMA genes. Given that peloric flowers in foxgloves are often
terminal, rather than universal, I guess that the situtation in
foxgloves is morre complicated.
--
Stewart Robert Hinsley