The morning glory and bindweed family
Convolvulaceae is the family of the funnel and the twining stem. Its flowers are built to be thrown away, its climbing is hardwired down to the direction of the spiral, and one of its members has abandoned being a plant almost entirely.
around 60 genera
roughly 1,900 species
Worldwide, most diverse in the tropics
Everything in this guide that belongs to Convolvulaceae
A morning glory does not have five petals. It has one. The corolla is fused into a single continuous funnel with no seams and no separate segments, and the five faint radiating lines you can see on the face are the only evidence left of where the petals used to be.
That construction is what makes the bud so distinctive. Because the corolla is one piece, it cannot fold like overlapping petals; it has to be pleated and then twisted, exactly like closing an umbrella, into a tight spiral spear. Watching one open is watching that spiral run backward, and in this family it happens fast enough to see, over minutes rather than hours.
The family name comes from the Latin for to twine or to roll together, which covers both the stem and the bud. Any funnel flower on a twining stem with a spiraled bud is almost certainly in this family.
The whole family builds cheap flowers deliberately. A fused corolla is made in one piece, needs no separate petals to be assembled and attached, and can be dropped whole when it is finished. Many members shed the entire funnel intact, so the ground under a vine is littered with limp complete flowers rather than scattered petals.
That is a strategy rather than a weakness. A climbing annual has a short life and a lot of stem to cover, and the calculation it has made is to spend nothing on making any one flower last and instead to produce a fresh set repeatedly. A plant that keeps a flower open for a week has to build it to survive a week of weather. This family does not bother.
Opening is run by an internal clock rather than by sunrise. Plants kept in constant conditions go on opening and closing on approximately the right schedule for some days before the rhythm drifts, which shows the timing is generated inside the plant and merely corrected by daylight.
A twining stem circles as it grows, and the direction is fixed by the species. It is not a response to the sun, to the hemisphere or to the shape of the support. Members of this family consistently wind one way, and other climbing plants, hops being the standard counterexample, consistently wind the other.
It can be tested in an afternoon. Unwind a young shoot from its support and wrap it back on the opposite way, and over the following day or two it will unwind itself and go back around the way it was going. The growing tip sweeps in a slow circle, several hours to a revolution, feeling for something to touch, and the bias in that sweep is built in.
Dodder is in this family and it is barely recognizable as a plant. It is a mass of thin orange or yellow threads draped over other vegetation, with no functional leaves, no chlorophyll and, once established, no roots in the ground at all. It cannot feed itself and does not try.
A dodder seedling has a few days of stored food to find a host. It sweeps in a circle like any other member of the family, but it is not feeling for a support, it is smelling for one: the seedling grows toward airborne chemicals released by suitable host plants, and can be shown to choose between hosts by scent alone. On contact it winds on, drives structures into the host's plumbing, plugs itself into both the water supply and the sugar supply, and lets its own base wither away.
For a wider view of the neighborhood, this family sits in the same order as the nightshades, so potato, tomato and petunia are cousins.