The prepuna and higher puna of the Andean northwest encompass a range of extremely harsh, arid habitats that range from the cardón cactus valleys from Jujuy to La Rioja, to the highest bleak Altiplano vegetation below the permanent snow line. Everything that grows here must be able to cope with extremely impoverished soils, and a huge difference in day- and night-time temperatures. Prepuna habitat usually refers to the sparsely vegetated rocky gullies and highland meadows ( prados ) of the cordillera, and is found at altitudes of between 2000m and 3500m. You'll see bunch grasses, reeds and stunted queñoa trees, but the most distinctive prepuna plant is the candelabra cardón cactus (also called pasakán ), which indigenous folklore holds to be the reincarnated form of their ancestors. These grow in a fairly restricted range centred on the Valle Calchaquíes, and take a century to reach their full height of 10m. Their beautiful yellow flowers produce a sweet fruit, and though they are now protected, their strong, light wood was used in the past as a building material. The puna is found above 3400m, and is characterized by spongy wetlands ( bofedales ) around shallow high-mountain lagoons, and sun-scorched flat Altiplano pastures of tough, spiky grasses. On the higher slopes, you'll find lichens and a type of rock-hard cushion-shaped prehistoric moss called yacreta that grows incredibly slowly - perhaps a millimetre a year - but lives for hundreds of years. It has been heavily exploited - partly for making medicinal teas, but mainly because it is the only fuel to be found at these altitudes.