The willow and poplar family
Salicaceae is the family a florist buys for line rather than for flowers. It supplies branches, structure and the silver buds of early spring, and it also supplies the compound that became the most widely used medicine in the world.
around 55 genera
roughly 1,000 species
Worldwide, with the willows concentrated in the cold north
Everything in this guide that belongs to Salicaceae
Willows and poplars gave up on petals entirely. The flower is a catkin, a dense cylindrical spike of tiny flowers with no showy parts at all, and a tree carries either male catkins or female ones and never both. The sexes are on separate plants, which botany calls dioecious, so a lone willow in a garden can never set seed on its own.
Poplars take the wind route and release clouds of pollen, then follow it with the drifts of white fluff that give the cottonwoods their name. Each of those tufts is a seed with a parachute of hairs. Willows hedge their bets: many of them are worked by early bees as well as by wind, which is why a willow in flower in March hums, and why willow is one of the first real nectar sources of the year in a cold climate.
The seeds are viable for a matter of days rather than years, which is part of why this family propagates itself so heavily from broken pieces instead.
Chewing willow bark for pain and fever is recorded in Sumerian, Egyptian and Greek sources, and it worked. The active material is salicin, isolated in 1828 and named directly after Salix, the willow genus. Meadowsweet supplied a related compound, and the two lines of work met in the 1890s when a modified version, acetylsalicylic acid, was made stable and gentle enough on the stomach to sell. It went on the market as aspirin.
Salicylic acid is still doing a job in the living tree. It is one of the signaling compounds a plant uses to switch on its own defenses when attacked, so the willow was never producing it for anybody's headache.
The same chemistry has a practical side in a workroom. Willow water, made by soaking cut willow stems, is an old and genuine rooting aid: the stems leach both salicylates and natural rooting hormones. It is a real effect and not folklore, though it is weaker than a commercial rooting compound.
The silver catkin everyone buys is a stage rather than a flower. It is the male catkin still enclosed in fine silky hairs, caught in the short window after the bud scale has been pushed off and before the flowers inside open. The hairs insulate the developing catkin against frost, which is how a plant gets away with flowering that early.
Left warm, it keeps going. The catkin lengthens, the anthers push out, the whole branch turns yellow with pollen and then sheds it over everything underneath. That is the natural next step and there is no stopping it, only slowing it: keep the branches cool and out of water and they hold the silver stage for weeks. Put them in water in a warm room and you have a few days.
Branches held dry at the silver stage will stay that way more or less indefinitely, which is why they are sold dry as often as fresh.
Willow is the easiest woody plant in the world to strike from a cutting. A stem stood in water will produce roots without any help at all, often within a couple of weeks, and curly willow left in a vase long enough will root and then leaf out. Customers find this delightful and it is worth mentioning, since a branch bought as decoration can become a tree in a bucket.
It also means the water fouls. Rooting stems shed material into it, so change the water rather than topping it up, particularly if anything else is sharing the vase.
Curly willow is the other way this family earns its place. The stems are genetically contorted rather than trained, they hold their shape permanently, and they need neither water nor light once dried, which makes them one of the few things in a shop with effectively unlimited shelf life.
Most genera in this guide hold a single flower, so they are covered on that flower's own page. One genus in Salicaceae holds several and has a page of its own.