It's proliferation, caused by too much nitrogen fertilizer or cold temp. See below:

"Proliferation occurs when the plants apical cells multiply so fast that they do not stop dividing once a flower is formed, they continue to divide and produce new buds in the centre of the existing flower to which leads to the rather unusual image seen above on a Tequila sunrise this week.

The occurrence of proliferation appears to be quite random and the exact causes are not fully known. Links have been made with cold weather and late frosts in Spring as it usually occurs on the first flush of flowers and then subsequent blooms are fine."

https://apuldramroses.wordpress.com/2012/05/21/rose-proliferation/

Also called, "vegetative center," being usually cool weather related, too much nitrogen fertilizer, or a varietal trait. By varietal trait is meant that some varieties are more prone to proliferations than others. Some proliferations even grow what appear to be plantlets, and I bet under ideal propagating conditions can be coaxed into growing roots and become a new plant!

Moses