My Petrocosmea season starts with Petrocosmea iodioides, Petrocosmea sericea and Petrocosmea barbata.
For me it seems that the petals of P. iodioides and P. sericea are very similar. But the peduncle and the sepals of P. iodioides are very hairy. As well as the leaves of Petrocosmea iodioides.
Picture 3: Left Petrocosmea iodioides and right Petrocosmea sericea