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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