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Areole    [ Botany ]
Adjective: Areolar

Dictionary of botanic terminology - index of names

     
  An areole is a distinguishing  organ universal to the entire cacti family, it is a condensed lateral shoot from which originate flowers, branches, spines,  and (if present) glochids and leaves.  

[“Areole” is an English adaptation of the Latin “Areola” meaning a "tiny area" or an "open space"]

It is a distinguishing  organ universal to the entire cacti family.

Through evolution the cacti ancestors begin to shorten the interleaf spaces. Subtended  in the axil of each leaf there is a lateral meristem. In cacti, this lateral meristem (Areolar meristem) became the place from which branches, flowers, leaf and spines arise. It became the areole that is to say a condensed lateral shoot. Generally circular or oval, looks like a raised cushion-disc, often covered by small hairs or by dangerous tiny, hair-like glochids. In some species, the areole is borne on a podarium, the modified petiole of the obsolete, subtending leaf. The leaves usually are not present, if present , they are very small and quickly fall off,  only a few of the less ancestral species still produce wide leaves. They are found along stems and cladodes of the plant and sits on the ribs or on the top of  tubercles (or at their base). There are two types of areole: radial, (e.g. Epiphyllum) with spines  spreading star-like around the growth centre, and unilateral where the growth bud is above the spine cluster this can be seen in Thelocactus, and in Coryphantha in which  the flower is set on the upper side of the tubercle, sometimes on old plants with a visible groove running on to the spines. Mammillaria completes the separation by bearing flowers in the usually woolly bases of the spine-tipped tubercles. In some species areole proliferation leads to the lateral cephalia of several genera of columnar cacti, and to the big terminal cephalium of Melocactus.

 

 
 
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