• I can think of four common families that have tetragonal stems: * Lamiaceae (Labiatae), the mint family, * Lythraceae, the loosestrife family, * Rubiaceae, the madder family, and * Urticaceae, the nettle family. Of these, only the Lamiaceae can claim the four-angled stem as one of its most defining characteristics. I searched Watson and Dallwitz's The Families of Flowering Plants ( and found 18 other families that have young stems that are square in cross-section. These are: * Alzateaceae, * Batidaceae, * Buddlejaceae, * Cistaceae, * Crypteroniaceae, * Dipsacaceae, * Garryaceae, * Geissolomataceae, * Guttiferae, * Melastomataceae, * Oliniaceae, * Phrymataceae, * Polypremaceae, * Punicaceae, * Restionaceae, * Scyphostegiaceae, * Thurniaceae, and * Verbenaceae. If you find a plant with a square stem, chances are it's a mint. Otherwise, you have a fun little taxonomic mystery on your hands!

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