The Areole - Unique to Cacti ... 1/3
What's so special about the areole?
Areoles, a specialized Auxiliary Bud,
is a special vegetative feature that a cactus possesses, from it spines and hairs, new joints (or offsets) and flowers/fruit appear. It is THE defining feature of the cactus, no other plant family has it, except a few close relatives.
If the plant has an areole - it's a cactus!
Areoles have two meristems (buds or growing points) one that produces hairs or spines, and the other may produce an offset or flower when awakened.
The second meristem may either produce a flower bud or offset bud - not both, if an areole has produced a flower in the past it can't offset from that particular areole in the future. After an areole has produced a flower, it "dies" by corking and making no further growth.
What prompts an areole to form an offset is unknown, but it can be forced into producing one by cutting off the growing tip of the cactus, whereby it will form offsets lower down when originally it had no intention of doing this. This is probably by some biochemical message system in response to injury to the growing point.
In the giant saguaro (Carnegia gigantea) lower areoles do not produce offsets, offsets are not formed until it reaches a certain height and possibly flowered, but as above offsets cannot come out of an areole that has flowered.
The areole are easily detached, so when the areole is damaged or detached the stem is not opened and water inside does not evaporate or leak out through any open wound.
Areoles may be borne on the ribs or near the top of the tubercle protrusion or just below it. In Mammillaria the tubercles are split into the spine-bearing meristem at the tubercle tip and the flower or vegetative meristem in the base of the tubercles.
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