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Euphorbia abyssinica, E. confinalis, E. cooperi: Convergent evolution
Don’t you think this plant looks like a candelabra-shaped, branched cactus? Its thick
trunk and side branches are obviously used to store water, just as in a cactus. It has
no leaves, just thorns on small bumps on its ribs. So why not classify it as a cactus?
If we were to cut through the skin of this plant, a white, milky juice would appear.
It looks like liquid latex, and is poisonous. Cacti don’t have such juice, but it’s
characteristic of the genus Euphorbia, the wolf’s milk plant. This genus includes
1,500 species worldwide. Some African Euphorbia in particular have developed
water-storage structures that remind us of a cactus. This phenomenon, where plants from
completely different families look almost the same, is known as convergent evolution.
This occurs when plants develop similar strategies to cope with similar environments,
resulting in a similar external appearance.
So, while in America it’s cacti that store water in their trunks to survive in a dry
climate, in Africa it’s the genus Euphorbia.
When Euphorbia blooms, it’s immediately obvious that this is no cactus. Cactus
flowers are funnel-shaped and brightly-colored, while those of the wolf’s milk plant
are small and yellowish. They consist of a small cup containing several male flowers
and a single female one. The male flowers each bear only a single anther, while the
female flower consists of a round, tripartite ovary. On the upper edge of the cup, you
can see a small, glistening structure: These are the nectar glands.
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Euphorbia abyssinica, E. confinalis, E. cooperi: Convergent evolution (MP3, 721 KB)
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