The amaranth family
Amaranthaceae produces the most saturated colors on the bench. Amaranthus, celosia and gomphrena all come from it, and all three hold a depth of red and magenta that most flowers simply cannot reach. There is a specific chemical reason for that, and it is the same reason beetroot stains a chopping board.
around 180 genera
roughly 2,500 species
Worldwide, and unusually well represented on dry, salty and disturbed ground
Everything in this guide that belongs to Amaranthaceae
Most red and purple flowers take their color from anthocyanins, the pigments that color a rose or a delphinium. This family does not use them at all. It uses betalains instead, and it is one of only a handful of plant groups that does.
Betalains are nitrogen based and produce a denser, more opaque color than anthocyanins manage. That is why a celosia red looks almost artificial, and why amaranthus reads as a rope of solid color rather than a scatter of petals. The two systems are mutually exclusive: no plant makes both.
The same pigment is what makes beetroot juice so hard to get out of a shirt, and it deserves a word of warning before a wedding. Deep red amaranthus or celosia against pale fabric can mark it, especially if the stems are still damp.
Look closely at any of these and the showy part is not petal tissue. Amaranthus and gomphrena carry tiny flowers wrapped in colored papery bracts, and the bracts are what you are buying. Celosia is stranger still: the crested forms are a growing tip that has flattened and fanned instead of forming a normal spike, and the brain-like shape is that fault bred deliberately into a feature.
Bracts are structural rather than delicate, which is why vase life here is good. Ten days to a fortnight is normal, and the color does not fade the way a petal does because nothing fragile is holding it.
It is also why they dry so well. Gomphrena keeps its color for years and celosia holds its shape completely. Hung upside down somewhere dark and dry, they need nothing else at all.
The stems are thick, soft and full of water, and they foul a vase faster than most. Amaranthus is the worst of the three because the trailing forms carry so much weight and leaf. Strip everything below the waterline and change the water rather than topping it up.
Trailing amaranthus needs planning more than care. A long stem will keep growing toward the light after it is arranged and can shift the balance of a design over a couple of days, so it wants placing where a little movement does not matter.
All three handle heat better than almost anything else a florist carries, which is a genuine advantage for a summer event. Where a rose collapses in a marquee, celosia and gomphrena carry on as though nothing has happened.
Beets, chard, spinach and quinoa are all in this family. So is the sugar beet behind a large share of the world's sugar, and so is the tumbleweed of the American west, which is a Salsola rolling its seed across open ground.
That mixture is not accidental. This family specializes in ground other plants find difficult: salt, drought and disturbance. A good number of its members are halophytes, able to grow in salt levels that would kill most crops outright.
Amaranth grain is one of the oldest cultivated foods of the Americas and was a staple across Mesoamerica before Spanish colonists suppressed it for its role in religious ceremony. It has returned as a gluten free grain, so the same family is now sold both as a health food and as a florist's trailing stem.