You will only catch this flower open at the edges of the day. The white trumpet unfurls in the late afternoon, holds through the night, and by mid-morning it has gone slack and furled. The bloom runs 6 to 7 inches long and about 5 inches wide, and it shuts just as the rest of the desert wakes into its heat. Nothing else here opens a white night-trumpet at that size. Photographed close, that one flower is the whole identification.
This is very likely the most dangerous plant on this bajada. Every part of it is poisonous: leaf, flower, seed, root. It carries tropane alkaloids — scopolamine, hyoscyamine, and atropine — and their concentration swings so far between plants, parts, and seasons that the distance between a dose that does something and a dose that harms or kills cannot be judged by eye. No preparation makes it safe. People are hospitalised and killed by it in Arizona, disproportionately the young, usually after reading something and deciding to try. It is worth keeping away from children, and from livestock on poor pasture, where a hungry animal makes a bad decision. Its ceremonial history in the Southwest reaches back some 3,000 years, always carried with specific, inherited knowledge, and none of that knowledge transfers. Admire it as history; do not audition for it.
A plant that blooms only through the night has arranged its life around the dark. It opens at dusk to aim the flower at the animals that fly after nightfall. Each bloom pools a heavy load of nectar, about 25 percent sugar, enough to hold a moth hovering for 10 to 15 minutes. The pale funnel stands out in the last light, and the nectar is what the plant offers for the visit. Look for the low, sprawling grey-green mound, up to 6 feet across, on graded edges, wash margins, and the two-track rather than out in undisturbed blackbrush. This is a plant that follows disturbed, sandy ground.
The night-flier that arrives is mostly one animal. More than 75 percent of the visitors researchers counted were a single hawkmoth, Manduca sexta, the Carolina sphinx, which hovers at the flower like a hummingbird and reaches in with a long, unrolled proboscis. The tidy version stops there. What it leaves out is that the same moth lays its eggs on the leaves, and the caterpillars that hatch eat the plant; one larva can strip 1,400 to 1,900 square centimeters of leaf before it is done. The adult moth takes nectar from the flower, and its larvae take the leaves, so the same insect draws on the plant twice over.
When no flower is open, read the pod: a round, spiny green capsule nodding on the stem. That thorn-apple is the plant.