The 1.30 update is here: Party Dungeons! Achievements! Arcade! Lava has requested a few things remain hidden for a week or two so everyone can get first time experience. NOTE: The Web version is not yet updated. There are a few lingering issues Lava needs to fix before that happens.
It's often misunderstood that this is part of the spore's head. But it's actually just a stylish hat. ... well, stylish in Mushroom Culture at least.