Certain North American cactus and South American euphorbias look almost identical. Plants can only respond to changes in their environment in certain limited ways. Similar changes tend to produce similar responses. When vast areas of the world began drying up several million years ago, native plants had to adapt or perish. So unrelated plant families in North and South America, Asia, Africa and Australia evolved independently to cope with their new desert habitats.
One of the ways plants survive on the desert is storing water in succulent stems, leaves, and even roots. Regardless of which desert they inhabit the plants that adapted for water storage eventually evolved similar shapes. We call this “Convergent Evolution”.
Another form of “convergent evolution” in desert plants is old world aloes and new world agaves. These succulent families have many known members including aloe vera and the “century plant”.
We can see that both cacti and euphorbias developed succulent stems and leaves. They also evolved extensive shallow root systems to collect even small amounts of moisture from the soil after a brief rain. Both kinds of plants developed spines, in part to protect them from nibbling animals and to shade themselves from the desiccating rays of the sun. Other forms of euphorbias and cactus like “living stones” resort to protective camouflage, or may be bitter or even toxic.
The cactus family has about 2,000 species and occurs naturally only in North and South America. The huge euphorbia family with 7300 species is found worldwide. Botanists distinguish the two by the shape of their flowers and seed pods.
|Botanical Name||Common Name||Family|
|Aloe vera||Medicinal Aloe||Xanthorrhoeaceae|
|Echinocereus pentalophus||Lady Finger Cactus||Cactaceae|
|Euphorbia ammak Variegata||Variegated African Candelabra||Euphorbiaceae|
|Euphorbia caput-medusae||Medusa Head Euphorbia||Euphorbiaceae|
|Euphorbia ingens||Candelabra Tree, Naboom||Euphorbiaceae|
|Euphorbia milii||Crown of Thorns||Euphorbiaceae|
|Euphorbia nerifolia||Indian Spurge Tree, Oleander Spurge||Euphorbiaceae|
|Euphorbia officinarum ssp. echinus||Euphorbiaceae|
|Euphorbia pseudocactus||Zig-Zag Plant||Euphorbiaceae|
|Euphorbia rigida||Gopher Plant||Euphorbiaceae|
|Euphorbia royleana||Danda Thor, Churee||Euphorbiaceae|
|Euphorbia tirucalli||Pencil Euphorbia||Euphorbiaceae|