The vegetation on the western side of the island is much less dense, often appearing as scattered clumps of trees on savannah-like plains rather than continuous forest; while in the south-west, where the rainfall is very scanty, the vegetation is largely of fleshy-leaved and spiny plants - aloes and cacti (the latter introduced), with several species of Euphorbia, as well as numerous lianas, one of which (Intisy) yields india-rubber.
The Cacti may be described in general terms as plants having a woody axis, overlaid with thick masses of cellular tissue forming the fleshy stems. These are extremely various in character and form, being globose, cylindrical, columnar or flattened into leafy expansions or thick joint-like divisions, the surface being either ribbed like a melon, or developed into nipple-like protuberances, or variously angular, but in the greater number of the species furnished copiously with tufts of horny spines, some of which are exceedingly keen and powerful.
In ascending from the coast-valleys there is first an arid range, where the great-branched cacti rear themselves up among the rocks.
Proceeding southward cacti become common, first a dwarfed species, and then a larger columnar form (Cereus quisco).
Palms are common, the chestnut abounds in many places, the cacti are almost as numerous as on the open plateau.
The predominating species is the chanar (Gurliaca decorticans), which produces an edible berry, and occurs from the Rio Negro to the northern limits of the republic. Huge cacti are also characteristic of this region.
Giant cacti and spiny scrub abound.