In message , Jan De Laet
writes

As anyone who has ever used identification keys surely is aware, it
happens rather frequently to find, e.g., a few tetramerous flowers in
inflorescences that have otherwise tens of pentamerous flowers and
stuff
like that. Some documented examples that illustrate such things can be
found below.


I've been taking note of aberrations among mallows. See

http://www.malvaceae.info/Biology/Aberrations.html

I've seen flowers with between 3 and 9 petals. What makes the situation
potentially worse for identification purposes is that the aberrations
are concentrated among the earliest flowers, so there may not be a
normal flower visible to give the game away.

Sidalcea seems to throw up hexamerous flowers more commonly that
tetramerous ones.
--
Stewart Robert Hinsley