Euphorbias attain great size and orchillas are characteristic of the forest weeds.
Vegetation is, however, tolerably abundant - tamarisks, oleanders, kafas, euphorbias, the milk bush, rhamnus and acacias being the most common and most characteristic forms of vegetable life, and pools of water are frequent.
Thorny acacias, euphorbias and aloes are still, however, found in patches on the plains.
In the northern temperate zone we find forests of a single species, others of three or four species; in this great tropical forest the habit of growth is solitary and an acre of ground will contain hundreds of species - palms, myrtles, acacias, mimosas, cecropias, euphorbias, malvaceas, laurels, cedrellas, bignonias, bombaceas, apocyneas, malpigias, lecythises, swartzias, &c. The vegetation of the lower river-margins, which are periodically flooded, differs in some particulars from that of the higher ground, and the same variation is to be found between the forests of the upper and lower Amazon, and between the Amazon and its principal tributaries.
The nearly related Ficoideae replace the new-world Cactaceae, but the habit of the latter is simulated by fleshy Euphorbias and Asclepiads, just as that of A gave is by the liliaceous Aloe.