No.4 is definitely 100% a chrysanthemum. Sorry to anyone in the Dahlia camp
I may not know much about photos yet, but do I know my flowers - I worked part time in a florist's when I was in college.
LOL - at least I can be of some use on the forum, even if it's not directly related to photography !
Dahlias and Chrysanths are quite closely related. They're both in the same family (along with Asters and weirdly enough Dandelions
) so the flower heads on some of the double blooms do look very similar.
The main classification difference is geographic origin. Dahlias are indigenous to South America and Chrysanths to the Far East and India, but there are subtle differences in stem and leaf shape too. The rounded leaf shape in photo no.4 screams "Chrysanth".
Unless they were bought in a specialist florist's, you can almost guarantee that they'd be Chrysanths anyway. Dahlias are quite hard to come by in your regular high street florist's but Chrysanths are everywhere. Florists used to refer to them as AYRs because at one time they were the only flower available to UK florists
All
Year
Round.
p.s. Forgot to say - I love the photo of the Gerbera !