Madagascar's ultramafic soils
On ground so rich in metal it poisons most plants, a few endemic specialists have learned to pull nickel into their leaves. A living chemistry found almost nowhere else, and barely studied.
Soils that kill most plants
Ultramafic rocks, peridotite and serpentinite, weather into soils loaded with nickel, chromium and cobalt, and starved of calcium, phosphorus and nitrogen. To most plants they are simply poison. In Madagascar these outcrops dot the central highlands and parts of the east, each one an island of endemic plants that grow nowhere else, because almost nothing else can grow there at all.
Hyperaccumulation
A hyperaccumulator is a plant that draws a heavy metal out of the soil and concentrates it in its leaves, far above the level in the ground it stands on. Some Malagasy species carry more than 10,000 parts of nickel per million in their leaf tissue, where an ordinary plant carries less than one. That is not something happening by accident. It takes an active, energy-hungry machinery of metal transporters and chelating acids to move that much metal and store it safely.
Why a plant would want a leaf full of nickel is still debated. The leading idea is defence: tissue that toxic is poison to insects and disease. Whatever the reason, the result is one of the most remarkable pieces of chemistry in the plant kingdom.
A plant that fills its leaves with nickel, on ground that would kill a wheat field, is one of the strangest things evolution has built. And almost no one has looked closely at how it does it.
Unlike anything else
The metal-handling systems in Madagascar's ultramafic plants are not variations on a familiar theme. They are different from the systems in Europe's serpentine flora and from those in New Caledonia, because Madagascar's outcrops, and the endemic families that colonised them, are its own. Studying them would be a first look at a way of living that exists on this island and almost nowhere else.
Fewer than a handful of these species have ever been examined in any depth. They sit on fragile, unstable ground that is easily disturbed. Understanding what grows on Madagascar's ultramafic soils, and how, is a piece of the living record that is both extraordinary and almost entirely unread.