The most common plants of the Mexican plateau are the agaves, yuccas and cacti, each of which is represented by a number of species.
Giant cacti and spiny scrub abound.
In ascending from the coast-valleys there is first an arid range, where the great-branched cacti rear themselves up among the rocks.
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.
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.
Truncatum the flowers have a very different aspect from that of other Cacti, from the mouth of the tube being oblique and the segments all reflexed at the tip. The short separate pieces of which these plants are made up grow out of each other, so that the branches may be said to resemble leaves joined together endwise.
Plantations of the nopal and the tuna, which are called nopaleries, are established for the purpose of rearing this insect, the Coccus Cacti, and these often contain as many as 50,000 plants.
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.
It consists of the females of Coccus cacti, an insect of the family Coccidae of the order Hemiptera, which feeds upon various species of the Cactaceae, more especially the nopal plant, Opuntia coccinellifera, a native of Mexico and Peru.