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Euphorbiaceae
This bench consists almost entirely of Euphorbia species
from the desert regions of Africa where they occupy the same
ecological "niche" as the cacti of the New World deserts.
Compare growth forms here with those of the cacti in the center
island. The convergence is truly amazing. If in doubt as to whether
it is a cactus or a euphorb, note that the Euphorbias have
a pair of stout spines (modified stipules) while the cacti usually
have more than two spines in their areoles. Also, a Euphorbia
will have milky juice while only a few cacti do. When
the plants are flowering, of course, there can be no confusion
between the small flowers in complex inflorescences in Euphorbia
and the usually large single flowers in the cacti. It
should be kept in mind that the euphorbs and cacti are quite
far apart in Angiosperm phylogeny and that the striking convergences
are entirely independent. Note Euphorbia Milii which
is at approximately the same evolutionary stage as the genus
Pereskia in the Cactaceae.
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