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Tubercle  [ Botany ]

Dictionary of botanic terminology - index of names

  A tubercle is a small raised area or nodule on a plant surface  

A small rounded projecting, part or outgrowth, (for example such certain leaf surfaces or on the lip of certain orchids, or the wart-like excrescence on the roots of some leguminous)
Tubercle (In cactus stems)  [ Botany ]
  Tubercle or podaria are conical cone-shaped protuberance that cover the stem of most of the more-or-less barrel or ball shaped  cacti.  

Very long tubercle of Astrophytum caput-medusae

A tubercle (or tubercule)  is an enlarged modified specialized leaf base, or petiole, and adjacent stem tissues fused together (podarium), the corresponding leaf of which no longer existing. Thus, the leaf base functions as the photosynthetic or food-producing part. The remaining leaves are the ones that are modified into spines. The spines radiate from a type of reduced bud peculiar to cacti known as an areole usually located at the tip of each tubercle like in Mammillaria.
The tubercles in most of the globose cactus are spirally-arranged. Otherwise the tubercles in some species can coalesce end to end in a continuous line forming ribs, ( example of ribbed cactus are Echinocactus and Cereus ) There is also a number of intermediates in between where tubercles may line up and form rows, or conversely ribs may discontinue to form distinct tubercles at the extreme examples with many combinations between the extreme examples.
Tubercles range from long and leaf-like - the extreme being Leuchtembergia and Astrophytum caput-medusae which looks more like an Agave than a cactus and to broad and shallow like Turbinicarpus and Lophophora. In some species the tubercles are provided with an adaxial furrow which extends nearly to the base
(for example Coryphantha spp., Ariocarpus kotschoubeanus).
The tubercle, and the rib in columnar cacti, are expandable to allow the cactus to store water during times of plentiful rainfall. In times of drought, these organs contract.

Tubercle of Ferobergia cv. Violet.






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