
Suzanne O. answered 12/02/19
International Experience and Multiple State Certifications
Hi Soma.
You may not like this answer. From what I have seen, there is no quick, one-stop place to find what you are looking for.
With that said, you can easily find images for the Genus of each of your flowers through Google by using the search terms: flower cross section (GENUS).
example: flower cross section iris
BTW: lilac is Syringa.
You can also try the search terms: structural botany.
To get more specific than that, you will have to hit the books, real or virtual.
I know that everyone uses online sources nowadays, so one that I found that might help a bit is Morphology of flowers and inflorescences by F. Weberling, found here: https://books.google.com/books?id=-ZlOAAAAIAAJ&printsec=frontcover&dq=botany+flower+cross+sections+reference&hl=en&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwj3wszw_JXmAhUCc98KHQTPADA4ChDoATACegQIAhAC#v=onepage&q&f=false
A good general reference for identification is from the American Horticultural Society, the Encyclopedia of Plants and Flowers by C Brickell: https://books.google.com/books?id=d-BgPoWCQowC&printsec=frontcover&dq=botany+flower+cross+sections+reference&hl=en&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwj3wszw_JXmAhUCc98KHQTPADA4ChDoATAIegQIBBAC#v=onepage&q=botany%20flower%20cross%20sections%20reference&f=false
You can also search in Elements of Structural and Systemic Botany by D. Houghton Campbell at Project Gutenberg: https://www.gutenberg.org/files/20390/20390-h/20390-h.htm.
You can also try the Botanical Society of America's plant image & media collection: https://cms.botany.org/media/collection/id.8.html
Happy hunting!