Ein Weihnachtsstern (oder Adventsstern)

Or even "eine Poinsettie".

So there we have another German language anomaly - it's "der ....stern" for the two in the title but "die Poinsettie". 

So we have a plant that is masculine or feminine depending on what name you call it.

Imagine if that worked in Real Life.  You could cause havoc.

It's the First Sunday of Advent here in Germany, so I think the flower is somewhat appropriate.