Green toadstool question

[Sexytang]

I have a large toadstool that I’ve grown from around a inch in size now it’s 7-8” across and it stays flat doesn’t wrinkle like others I see why is this.

 

[Streetlamp]

Flow maybe? Just a guess

 

[Leslie Tabor]

I swear I responded to this yesterday??

 

[Sleeping Giant]

It stretches out, there's no obstacles in its way to make it curl up, mine does the same, its almost 18" across.