The orchid family
Orchidaceae is either the largest family of flowering plants on earth or the second largest, trading the title with the daisies depending on who is counting. One flowering plant in ten is an orchid, and the family got there by specializing harder than anything else alive.
around 750 genera
somewhere near 28,000 species
Every continent except Antarctica, richest in the wet tropics
Everything in this guide that belongs to Orchidaceae
An orchid flower has three sepals and three petals, and one of those petals is transformed into the lip, the broad landing platform that gives the flower its face. In the bud, that lip is at the top. As the flower develops the stalk twists through half a turn so that by the time it opens the lip has arrived at the bottom, where an insect can stand on it.
The twist is called resupination and you can see the evidence on any orchid on a bench: follow the little stalk behind an open flower and it is visibly turned. A few orchids skip it and hang their lip upward, and they look wrong in a way that is hard to place until you know why.
Everything about the lip is aimed at one specific visitor. Orchids imitate female insects, rotting meat, other flowers' nectar and the scent of a bee's own territory markers, and a great many of them offer no reward whatever. Roughly a third of the family gets pollinated purely by deception.
In almost every other flower the male and female parts are separate structures. In an orchid they are fused into a single organ called the column, standing in the center of the flower above the lip, with the stigma on one face and the pollen at the tip.
The pollen is not loose. It is bound into waxy masses called pollinia, usually two or four of them, often with a sticky pad attached. A visiting insect touches the pad, the whole parcel comes away and rides off glued to its head or back, and it is delivered complete to the next flower. Nothing is spilled and nothing is wasted, and a single visit can pollinate every ovule in the flower at once.
That efficiency is the trade the family made. An orchid can afford to rely on one rare and specific pollinator because when it does arrive, one visit is enough.
An orchid capsule can hold a million seeds or more, and each one is microscopic, little more than an embryo in a thin coat with no food reserve packed alongside it. On its own it cannot germinate. It has to be found by the right soil fungus, which enters the seed and feeds it until it can support itself, and the young plant is a parasite on that fungus for its first months or years.
This is why orchids defeated growers for a century. Seed sown in a pot did nothing, and every orchid in Victorian Europe was a plant torn off a tree in the tropics and shipped, with losses that emptied whole hillsides. Sterile flasks and a nutrient jelly solved it in the 1920s, and it is the reason an orchid is now a supermarket purchase rather than a fortune.
Vanilla is the exception that shows the rule. It is the cured seed pod of a climbing orchid, and outside its native Mexico its pollinator does not exist, so every vanilla pod in world trade is pollinated by hand, one flower at a time, on the morning it opens.
Orchid flowers last a long time, several weeks on a cut stem and months on a plant, because an unpollinated orchid has no reason to stop waiting. The moment it is pollinated that reverses. The flower has done its job, the plant withdraws support, and it wilts within a day or two.
The practical consequence catches people out. Knocking the pollinia off the column while handling a stem tells the flower the same story, and that bloom will collapse for no visible reason. Handle cut orchids by the stem and keep fingers out of the throat of the flower.
The same mechanism makes the whole family unusually sensitive to ethylene, because ethylene is the signal the flower is acting on. An orchid belongs nowhere near ripening fruit.
The other thing to understand about the family is where most of it lives. The majority of tropical orchids are epiphytes, growing on the bark of trees without taking anything from them, anchored by thick roots wrapped in a spongy white layer that soaks up rain and turns translucent green while it is wet. Those roots evolved to be drenched and then dried by moving air within hours. That is the entire explanation for why an orchid is sold in coarse bark instead of soil, and why leaving one standing in water kills it.