Wikipedia says

A regular triskaidecagon is not constructible with compass and straightedge. However, it is constructible using a Neusis construction.

Grapefruit trees know how to use neusis.

Triskaidecagon in an orange slice

 

As well as the unknown medieval architect that made the Cathedral of Larino.

Triskaidecagon in a rose window

 

And the Czech Republic coin makers.

 

Apparently, nobody else knows.

 

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