Cactus & Succulent Society
of New Zealand (CSSNZ)
The Areole - Unique to Cacti
What's so special about the areole?
Areoles, a specialized Auxiliary Bud,
is a special vegetative feature that ONLY cacti possess, 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.
If the plant has an areole - it IS 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 sort of "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 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 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.
Spines
Spines may be just the reason some people grow cacti!
They come in all sorts of flavours: Straight, Hooked, Curved, Twisted, Pectinate, Comb-like, Thick, Thin, Broad, Narrow,
Hard, Soft, White, Black, Coloured, Ridged, Smooth. Even absent altogether !!
Even on the same areole the spines may be different e.g.. a strong central spine surrounded by radial spines, or multi-coloured
like a rainbow (Echinocereus is an example).
The spine is probably a reduction of the leaf stalk through evolution to adapt to the drier conditions and/or give
armature to defend off animals. The spines and tuffs of hairs now also protect the
delicate meristem/growing bud below.
Opuntias have special spines called "Glochids" - and they are not to be messed with - they are small and barbed. A helpful
hint to get them out of the skin, if you are unfortunate enough to brush against an opuntia, is to place sticky tape/sellotape
on your skin and then pull it off, hopefully taking the glochids with them (a depilatory !?).
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