Purple Mushroom Coral ...happy but confused

Ive had a single mushroom coral for the past 7 months. There is a tiny new purple mushroom that is sprouting up about 3 inches away from it. It isnt a hitchhiker as Ive added nothing new in the past 4 or 5 months. The existing mushroom wasnt cut or split in any way. How do they reproduce? I cant seem to find this info online (yet). Thanks in advance for your info ...and Happy Holidays!

 

Part of the base will stretch out and attach away form the main organism and eventually a new head will form. Most noticeable when the mushroom is retracted.

 

Thanks for the info jonjon. It may be elementary to some, but this amazes me. This is the first thing in my tank that has appeared without having been purchased. A great christmas gift!

 

It is awesome. My first coral was a really nice mushroom. Still one of my favorite corals. It is about 4" now and is surrounded by about a dozen smaller ones.

 

I too, love my shroom, as basic as it is. It has awesome neon blue spots that the pic doesnt justice. My parameters are always on spot including trace minerals. Is there something more I can do to expediate population without splitting?