The pea and bean family
Fabaceae is the third largest family of flowering plants and arguably the most important one to agriculture, because of something it does underground rather than anything it does in flower. For a florist it supplies sweet peas and wisteria, two of the most heavily scented things available and two of the shortest lived.
around 765 genera
roughly 20,000 species
Worldwide, in nearly every habitat that supports plants
Everything in this guide that belongs to Fabaceae
The classic pea flower has five petals doing five different jobs. One large upright petal at the back is the standard, two at the sides are the wings, and the two at the bottom are fused into a boat shape called the keel, which hides the stamens and the style inside it.
Botanists call the arrangement papilionaceous, meaning butterfly-like, and it is a mechanism rather than a decoration. A bee heavy enough to land on the wings presses the keel down, which pushes the reproductive parts up against its underside. Light insects are excluded because they cannot trip it.
Look at a sweet pea, a wisteria floret, a broom flower and a runner bean flower side by side and the same machine is visible in all four. Wisteria hangs it in a raceme a foot or more long, which is simply the same flower repeated down a stem.
The reason this family matters beyond the garden is a partnership with bacteria. Rhizobia living in nodules on the roots take nitrogen straight out of the air and convert it into a form the plant can use, and the plant feeds them sugars in return.
Almost nothing else does this at scale. It is why clover is sown into pasture, why beans were rotated with cereals for centuries before anybody knew why it worked, and why legumes are so high in protein: they have a nitrogen supply other plants have to compete for in the soil.
For a gardener the practical version is that peas and beans leave the ground better than they found it, and sweet peas can be grown on poor soil that would starve a comparable annual.
Sweet peas last three to five days and wisteria two to four. There is no technique that changes this substantially, and anybody promising otherwise is selling something. These are thin-stemmed, soft-tissued flowers that were never built to be cut.
What you get in exchange is one of the best scents in horticulture. Sweet pea in particular is worth carrying purely for that, and it has the useful property of getting stronger as more stems go into a vase rather than turning cloying.
Cut them in the cool of the morning, keep them cold, and pick them hard: sweet peas flower more the more they are cut, because a plant allowed to set seed shuts down production. That is the one piece of advice that genuinely changes the outcome, and it is for the grower rather than the vase.
Peas, beans, lentils, chickpeas, peanuts, soybeans, alfalfa, clover, carob, tamarind and licorice are all in this family. So is the acacia, the mimosa sold in late winter, laburnum, lupins, broom and gorse. In terms of what people actually eat it is second only to the grasses.
It is also a family with a real toxic streak, and the two facts sit closer together than is comfortable. Laburnum seeds are seriously poisonous, wisteria seeds and pods will make somebody very ill, and even sweet pea seeds are toxic if eaten in quantity, causing a condition called lathyrism that has appeared in famine populations living on the related grass pea.
Nothing in a bouquet is a hazard by being looked at, but wisteria pods look like edible bean pods and are worth mentioning to anybody with children or a curious dog.