On the lower slopes of the Andes are found oak, beech, cedar, Winter's bark, pine (Araucaria imbricata), laurel and calden (Prosopis algarobilla).
The provinces of Santa Fe, Cordoba and Santiago del Estero are only partially wooded; large areas of plains are intermingled with scrubby forests of algarrobo (Prosopis), quebracho-blanco (Aspido-sperma quebracho), tala (Celtis tala, Sellowiana, acuminata), acacias and other genera.
The western dry areas have the old-world leguminous Astragalus and Prosopis (Mesquit), but are especially characterized by the northward extension of the new-world tropical Cactaceae, Mgmmillaria, Cereus and Opuntia, by succulent Amar llideae such as A gave (of which the so-called American aloe is a type), and by arborescent Liliaceae (Yucca).
In a few hollows which are reached by moisture the trees of the desert find support, the algarrobo (Prosopis horrida), a low tree of very scraggy growth, the vichaya (Capparis crotonoides), and the zapote del perro (Colicodendrum scabridum), mere shrubs.
The " tongue," for example, is short and obtuse or emarginate in Colletes and Prosopis, while in all other bees it is pointed at the tip. But in Andrena and its allies it is comparatively short, while in the higher genera, such as A pis and Bombus, it is elongate and flexible, forming a most elaborate and perfect organ for taking liquid food.
The kukui (Aleurites triloba) and the algaroba (Prosopis juliflora) are the principal species of forest trees that occur below elevations of 2000 ft.
The arborescent growth near the mountains is larger and more vigorous, in which are to be found the " algarrobo " (Prosopis siliquastrum) and " chanar " (Gourliea chilensis), but the only shrub to be found on the coast is a species of Skytanthus.
Another variety, obtained from the Prosopis dulcis, a leguminous plant, is called gum mesquite or mezquite; it comes from western Texas and Mexico, and is yellowish in colour, very brittle and quite soluble in water.