The mint and lavender family
Lamiaceae is the family you can identify with your fingers in the dark. Roll a stem between finger and thumb, and if it has four flat sides, if the leaves come off it in pairs, and if crushing one releases a scent, you are almost certainly holding a member of the mint family.
around 240 genera
roughly 7,500 species
Worldwide, with the greatest concentration around the Mediterranean
Everything in this guide that belongs to Lamiaceae
Two characters between them place most of this family, and neither needs a hand lens. The stem is square in cross section, with four distinct corners you can feel through a glove, and the leaves are set in opposite pairs, each pair turned a quarter turn from the one below it. Look down a stem from directly above and the leaves make four ranks.
The flower gives the family both its names. Each bloom is fused into a tube that opens into two unequal lips, an upper one usually hooding the stamens and a lower one spread flat as a landing platform for a bee. The older name for the family was Labiatae, from the Latin for lip, and it is still in use. Lamium, the genus the modern name is built on, is the unremarkable dead nettle of a hedge bottom.
The fruit is the third character and the least obvious. Every flower leaves four small dry nutlets sitting in the cup of the calyx, which stays on the stem after the petals have gone. It is why so much of this family holds its shape long after it has finished flowering.
Draw a thumbnail across a lavender leaf and the smell arrives at once. The volatile compounds are not locked inside the tissue; they sit in glandular hairs on the surface, small stalked reservoirs that burst under the slightest pressure. It began as a defense against being eaten, and it is the reason this one family supplies more of the world's culinary herbs than any other.
It also explains something every florist knows without knowing why. Oils do not evaporate the way water does. As a lavender stem dries the water leaves and the scent stays behind, so dried material smells as strongly as fresh and goes on smelling for months. Almost nothing else in the cooler behaves like that, and it is why lavender sells dried in volumes no cut flower could match.
Hang bunches upside down somewhere dark and dry with air moving through it. Light bleaches the color out faster than anything else does, and a bunch dried on a sunny windowsill will be gray inside two weeks.
The green bells are not flowers. Each one is a calyx, the cup that in an ordinary flower sits behind the petals and holds them, swollen here into a wide shallow shell about the size of a thumbnail. The real flower is the small white fragrant thing tucked down inside it, easy to miss and gone long before the bells are.
That is exactly why the stem lasts. Green tissue built as a protective cup is far tougher than petal tissue, so the display outlives any true flower on the bench. It is also nothing to do with Ireland. The name is about the color, and the plant comes from Turkey, Syria and the Caucasus.
Two working notes. There are small sharp spines hidden under the bells, so anyone who runs a hand down a stem the wrong way does it once and never again. And the stems are strongly geotropic: leave a box lying flat overnight and every tip will have turned upward permanently by morning. Store them standing.
This is the herb family. Basil, mint, rosemary, thyme, oregano, marjoram, sage and savory are all Lamiaceae, and so are catmint, monarda, coleus and the enormous genus Salvia, which runs to something like a thousand species on its own and covers both the scarlet bedding plant and the sage in a stuffing.
The overlap is useful rather than trivial. Anything out of this family behaves in water the way a woody Mediterranean plant behaves, which means it wants a shallow drink and not a deep one. Lavender, rosemary and sage stems rot if the lower third is submerged, and a rotting stem fouls the water for everything standing beside it.