Many possess thick water-storing parenchyma cells in their stems or leaves, and are succulent, like the agave and the cactus.  
They can be split up into two varieties: obligate ones are limited to the namesake pathway, while facultative ones are not and only rely on it during times of environmental stress. One can identify them by measuring the difference in the amount and the acidity of malic acid in their tissue between morning and evening.  Many possess thick water-storing parenchyma cells in their stems or leaves, and are succulent, like the agave and the cactus.  FTP, identify this type of plant that opens its stomata during the night time to take in CO2, unlike its C3 and C4 counterparts.
They can be split up into two varieties: obligate ones are limited to the namesake pathway, while facultative ones are not and only rely on it during times of environmental stress.
CAM (or Crassulacean Acid Metabolism) Plants