Exhibit A, m'lud:
A stem of common or garden Mint - Mentha spicata. This is the one you probably have growing in your garden - the one that you are advised to grow in a pot, or with a barrier around it, to stop it taking over your entire garden.
What shape would you call that stem? Square. Definitely square. Not square-ish, Nice flat sides, sharp crisp corners - it's square.
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