When I tried to collect petals by releasing Pikmin with a certain flower type, I did not receive any, or they are not showing in the petal menu.
In this case, I need Red Hibiscus petals for the event challenge. I gave a Pikmin Red Hibiscus nectar, collected the single petal, then released the Pikmin from the menu. The screen displayed the Red Hibiscus icon and “+10”, but when I checked my petal collection, I had 9, from the 8 that I started with and the single petal I had just collected. I tried again with another Pikmin, and the same thing happened. 
Sadly, released pikmin only return regular petals white, red, yellow, or blue. So if you release a red hibiscus pikmin you get 10 plain red petals.
Oh, I see. Thank you.