|Photo by Ned Harris 1/17/2013|
Great info of the mighty Saguaro (Carnegiea gigantea) here from - you guessed it - Saguaro National Park. The answer to the question: why the 'extra' pleat (above) must have to do with early growth. Remember, the top of the saguaro is the growing tip. The saguaro pictured must have signaled the need for an additional pleat as the space between the two pleats (previously) next to each other became too big. I expect there's a nice equation for this. See the galleries at this site for math-y plant growth 'stuff' (phyllotaxis, for all you nerds out there).
|Photo by Ned Harris 1/9/2013|
Saguaro between a rock and a hard place.
|Photo by Peggy Wenrick 1/26/2013|
The Velvet Mesquite (Prosopis velutina) was the 'nurse tree' for the saguaro; now the saguaro is returning the favor of shade to this Fishhook Pincushion (Mammillaria grahamii).