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Cactus
By Joe Wolf
Polk County Master Gardeners
Cacti are an interesting and diverse group of
plants. Cacti are one example of succulents. All
cacti are succulents, but not all succulents are
cacti. Any plant with thick, fleshy leaves, stems,
or roots that hold water is a succulent. Most
succulents come originally from hot, dry places
that only get water intermittently. In order to
survive, they must collect the sparse rainfall and
store it. The differences between cacti and
succulents will be discussed later in the article.
There are between one thousand and two
thousand species of cacti. But, there are many
more thousands of succulents that are not cacti,
Cactus flower
although we may call them that. For example,
the plant ‘crown of thorns’ is not a cactus, even though it has large, sharp thorns. Other examples of
succulents are the jade plant, the century plant, kalanchoe, agave, yucca, aloe, and bromeliads. The
prickly pear and the Christmas cactus are two of the few cacti in Florida with a common name. But all
cacti have scientific names.
All cacti are all in the Cactaceae family. They come in many shapes and sizes. Some cacti are tall and
straight with no of a few branches, while others are like small round rocks growing close to the ground.
Some are like barrels, some small and some large, sometimes growing singly and sometimes bunches of
them tightly grouped together. Some cacti are flat, some rope-like, while others are round like balls.
Spines may be many or few. All cacti, except one (Rhipsalis baccifera subsp. horrida), grow only in the
Americas (North, South,
Central and the Caribbean), at
least before people started
moving them around the world
for their gardens. All of them
are stem succulents: they store
water in their stems and
nowhere else. Most do not
have what we consider leaves.
Barrel cactus
The leaves of cacti have, over
the millenniums, become
highly modified into spines.
Without leaves, cacti do photosynthesis in their
stems. Most cacti live in hot arid climates with
high daytime temperatures and low nighttime
temperatures. A few cacti live in the South
American rain forests. Many of these are long
and thin and grow in trees.
What separates cacti from other succulents with
spines or thorns? The primary difference is in
the placement of the flowers and spines. These
features are grouped in small pads called spine
cushions, or areoles. Even cacti without spines
Cactus garden in a low pot
have areoles. All cacti, and only cacti, have
areoles. Areoles are a small radial structures, which are arranged in a regular pattern, usually along
either a rib or equally spaced on the face of the cacti. An exception to this rule is the Christmas cactus.
In that cactus, the areoles, with their spines and flowers, are on the tips and edges of the flat stem. A
second difference is that the flowers of cacti are different from all other flowers. They are unusually
conspicuous. The differences between the cacti flower and other flowers is very technical, it involves
the structure of the parts of the flower. We cannot go into those differences here without explaining a
great deal of technical information.
There is only one cacti native to Polk County, the prickly pear or Opuntia humifusa, but there are
thirteen others native to other parts of Florida. There are other members of the Opuntia genus that are
native to much of the continental United States. Of the species native to Florida, at least two are
endangered. One of those is called “Queen of the Night” because it blooms only at night. It has a
wonderful perfume that it uses to lure pollinators. Another species grows in trees and is rope-like. It
can grow up to 23 feet in length. There are several other cacti that grow well here in Florida. Most do
better in South Florida because they are sensitive to freezes.
Cacti can be planted in beds, either singly or in groups. Often the space between the individual plants is
covered with small stones or a groundcover. The ground must be allowed to dry out so moisture
retaining mulch is not a good idea. Another way to
plant cacti is in containers, usually shallow ones like
hypertufa pots or bonsai pots. Arrangements of cacti
in containers can be beautiful, but do require
maintenance as some cacti grow large. Cacti can be
difficult to handle because of their spines. Heavy
gloves are a necessity when working with cacti.
Cacti can be a really interesting plant to grow, either
in a cactus garden or in containers. They don’t
require much maintenance, are extremely drought
tolerant, and many can stand the hottest sun.
Cactus for sale at Bok Tower
For more information on cactus see the following articles.
http://cactiguide.com/distribution_display/?state=Florida,
https://edis.ifas.ufl.edu/ep326,
http://aggie-horticulture.tamu.edu/databases/cactus/growingcactus/,
http://www.eoearth.org/view/article/53cebc870cf2d022a359c880/,
http://okeechobee.ifas.ufl.edu/News%20columns/Prickley.Pear.htm