Typified by its brush scrub and wiry grassland, the Patagonian steppe ( estepa ) covers the greatest extent of any Argentine ecosystem. This vast, grey-brown expanse of semi-desert lies to the south of the pampas grasslands, to the east of the Andean cordillera, and as far south as Tierra del Fuego, and includes areas of genuine desert and cracked, dessicated meseta. Vegetation is stunted by the poor, gravelly soils, high winds, and lack of water, except along the few river courses, where you find marshlands ( mallines ) and startlingly green willows ( sauces ). Just about the only trees apart from the willows are the trademark, non-native Lombardy poplars, planted to shelter estancias. The habitat itself can be broadly grouped into brush steppe , which frequently forms part of the brief transitional zone between the more barren lands to the east and the cordillera forests; and grass steppe , typified by tussocks of yellowy-brown coirón grass, usually closely cropped by sheep. Much of the scrubby brush is composed of monochrome mata negra , but in places, you'll come across the resinous, perfumed mata verde , or the manicured ash-grey mata guanaco , which blooms with virulently orange flowers. You'll also see spiky calafate bushes, and the duraznillo , which has dark green, tapered leaves. One of the largest bushes is the molle , covered with thorns and parasitic galls. The adhesive qualities of molle sap was once utilized by indigenous peoples to fix arrowheads and scrapers to their wooden shafts, but nowadays the most common use for this bush is as firewood to prepare an aromatic asado . Smaller shrubs include the silver-grey senecio miser ; compact, spiky neneo plants; and the lengua de fuego , a dull-grey shrub with bright-red flowers when in bloom. In moister areas, you'll find the colapiche , whose name ("armadillos' tail") comes from the appearance of its smooth, leafless fronds.