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Cactus are as
evocative of the West as Sagebrush; the two even often grow near each
other. Cactus are indigenous to the Western Hemisphere, are found in
their greatest concentration along the Tropics of Cancer and Capricorn,
and are native to every American state except Vermont and Maine. They are
found in deserts, on seashores, in mountains, on plains, balds, and
glades.
Cactus come in a number of
shapes, their flowers are often very large and attractive, their fruits
are edible (some delicious, some not so), and they have
evolved a number of structures and processes that make them perfectly at home in what we humans
usually call "a hostile environment": They have a tough, waxy
outer layer that reduces moisture loss; they produce chlorophyll not in
leaves but in the outer cells of the stems; they convert absorbed water
into a mucilaginous liquid that can be stored in large quantities in
tissues capable of expanding; many Cactus root easily into new plants
from broken pads/stems of older plants.
"Cactus"
is Greek for "prickly plant"; the word was used by Linnaeus in
the 18th century to describe a prickly, thistle-like member of the
Asteraceae Family found in Italy. "Cactus" was then used in
the 19th century for the newly discovered spiny, drought resistant
plants discovered in the Western Hemisphere. |
