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Cladode   [ Botany ]
Phylloclade, Leaf-like branches, pad

Dictionary of botanic terminology
index of names

  A cladode is a stem modified for photosynthesis that looks like a leaf. It is flat for increasing the surface area, thick for storing water and green for photosynthesis.  
Cladodes are not leaves but swollen water-storing stem segments. In cladodes the leaves are often modified into spines, the function of spines is protection as well as to reduce transpiration. Axillary buds are modified into thin short and greenish structures. and cuticle is an outer covering which is present for preventing transpiration.
To identify and distinguish a phylloclade from a true leaf it is necessary to the observe the vegetative shoot, on which leaves are still present small or scale-like, and the leaves of these species (if present) are ephemeral and soon abscise (e.g. Opuntia).
Most genera of cladode-producing plants occur in the cactus family (Cactaceae). More than 200 in subfamily Opuntioideae. These are comparatively thick cladodes, with pads often exceeding one centimetre in thickness, and the flattened pads, also called joints, have nodes on the two flat surfaces as well as along the edges, arranged in a helical pattern. A narrow leaf forms at each node, and from the axillary bud forms a determinate short shoot (the areole) on which are produced modified  leaf primordia that are the spines. The foliar leaves soon abscise, leaving the spine-covered cladode to perform photosynthesis.
Flattened green stems also appear in more than a dozen genera of  epiphytes and hemiepiphytes cactus. Also referred to as 2-ribbed, most of these flattened stems have areoles arranged only along the two edges, not on the broad surfaces, although in the rhipsalid epiphytes this is not always true. In general the 2-ribbed epiphytic stems have evolved from species having three or four ribs on the stem, hence they formed via a different developmental and ribs on the stem, hence they formed via a different developmental and evolutionary sequence than did the platyopuntias. Some cactus epiphytes exhibit two, three, and four ribs on a single individual, and there commonly are differences in stem morphology from juvenile versus adult types.

(e.g. Zygocactus = christmas cactus)