The phlox family
Polemoniaceae barely left home. The great majority of the family grows in western North America and a large share of that in California alone, and it has become one of the standard textbook families for showing how a flower's shape is dictated by whatever is meant to visit it.
around 20 genera
roughly 400 species
Overwhelmingly western North America, with a few elsewhere
Everything in this guide that belongs to Polemoniaceae
Very few plant families are this geographically concentrated. Something like nine in ten species in this family are native to western North America, and the dry hills, deserts and mountains of California and the Great Basin hold more of it than anywhere else on earth. A handful of species reached South America and exactly one genus made it to Eurasia.
Much of the family is not the tall border plant people picture. A great many members are tiny desert annuals a few inches high, the kind of plant botanists have to lie down to look at, which germinate in numbers after winter rain, flower within weeks and are gone before summer. In a good year they color whole hillsides and in a dry year they simply do not appear.
Any family packed into one region like this tends to have diversified there fast and recently, splitting into many closely related species separated less by geography than by what pollinates them.
The flower shape is consistent across the family: a narrow tube, sometimes very long, opening abruptly into a flat face of five lobes, like a small tray set on a stalk. What varies, and varies enormously between close relatives, is how long that tube is and what color the face is.
Those two variables decide who can feed there. A short tube with a wide flat landing surface in white or pale blue is a bee flower. A long narrow tube, pale and heavily scented after dark, is built for a night flying moth that hovers and reaches in with a long tongue. A long tube in strong red, with no scent at all because birds hunt by eye, is a hummingbird flower.
This family is where that logic is most easily demonstrated, because species that are near identical in leaf and habit sit side by side on the same hillside with completely different flowers and completely different visitors. It is the reason Polemoniaceae turns up in every textbook chapter on the subject.
One member of the family takes that a step further and changes its mind. Scarlet gilia grows in the mountains of the American west and opens the season in deep red, worked by hummingbirds and by them almost exclusively.
Partway through the summer the hummingbirds move on south. The plants that are still flowering then produce paler flowers, pink and eventually close to white, which are much easier for hawkmoths to find in the dark. The population effectively hands itself from one pollinator to the next as the first one leaves, and the plants that make the switch set more seed than the ones that do not.
It is one of the more elegant results in field botany, and it is worth knowing because flower color is usually assumed to be a fixed property of a species. Here it is a response to who is still in the neighborhood.
The family name comes from the Greek for war, and the story behind it is that two kings each claimed to have discovered the medicinal value of the plant and went to war over the credit. Pliny reports it, which is not the same as it having happened, but it has given the family the most belligerent name in botany.
The genus in question is Jacob's ladder, named in turn for its leaves, which are divided into neat opposite pairs of leaflets running up the stalk in rungs.
The odd one out is the cup and saucer vine, a Mexican climber and by far the largest thing in the family, which throws a heavy stemmed flower the size of a fist. It opens green and musty smelling, which is not an insect signal, and turns purple over the following days. In its own country it is worked by bats, and everything about that first night, the size, the color, the smell and the quantity of nectar, is aimed at them.