The bellflower family
Campanulaceae is named for its shape and very little else needs saying about how to recognize it. Campanula means little bell, and the family delivers exactly that: fused petals forming a cup or a bell, usually in blue, violet or white, hanging or facing outward along an upright stem.
around 84 genera
roughly 2,400 species
Worldwide in temperate and subtropical regions
Everything in this guide that belongs to Campanulaceae
The defining feature is that the five petals are joined for most of their length rather than being separate. That fusion is what makes the bell, and it is why a campanula flower comes off the plant in one piece instead of shedding petal by petal.
The flowers are usually arranged up a single upright stem, opening from the bottom toward the tip over several days. That gives the same practical advantage as a gladiolus: the stem carries its own succession, so a spike keeps performing after the first flowers have gone, and removing spent bells as they finish keeps it looking intentional.
Trachelium takes the family in a different direction, massing hundreds of very small flowers into a flat or domed head rather than spacing them out. It reads at a glance as something from another family entirely, which is a useful reminder that head shape is a poor guide to relationship.
Cut a campanula stem and it bleeds a white latex. That sap is the family's characteristic and it is a nuisance in water: it clouds a vase quickly and can block the stem's own uptake as it congeals at the cut end.
The fix is straightforward. Cut the stem, let it stand in clean water for a short while so the initial bleeding settles, and change that water before arranging. Some growers sear the cut end briefly in boiling water, which stops the flow immediately and works well on the softer stems, though it is rarely necessary for a domestic bunch.
Vase life is decent once that is handled, a week to ten days for campanula and a little longer for trachelium. Both are better than their delicate appearance suggests, and both dislike being crowded in a bucket because the bells bruise against one another.
True blue is rare among flowers. Most of what gets called blue in the trade is really violet, mauve or a treated white, because the pigment chemistry to produce blue is difficult and few families manage it convincingly.
This one does. Campanula and trachelium both give a clear violet blue that needs no help, and lobelia at the deeper end is about as close to pure blue as a garden plant gets. For anybody building an arrangement where blue actually has to read as blue, this family and the delphiniums are the short list.
The color also holds in the vase rather than fading toward gray, which is not true of every blue flower. That makes campanula more useful in a long-lived design than its reputation as a cottage garden filler would suggest.
Canterbury bells are the classic garden member and have been grown in Europe since at least the sixteenth century. The harebell, the Scottish bluebell, is a wild campanula, and it is a different plant entirely from the English bluebell, which is not in this family at all. The two names cross over between England and Scotland and cause endless confusion.
Lobelia belongs here too, both the trailing bedding kind and the tall cardinal flower. Rampion, a campanula grown for its edible root, is the plant at the center of the Rapunzel story: the girl is named after the vegetable her mother stole from the witch's garden.
Beyond rampion there is almost nothing edible in this family, and several members are mildly toxic. The milky sap is the clue, as it so often is.