**3. Discussion**

Guralnick and Jackson [10] previously suggested the CAM pathway appeared evolutionarily first in the leaf and the C4 photosynthetic pathway overlaid the CAM tissue. These conclusions were supported by research which showed the CAM PEPCase gene was more primitive to the C4 derived PEPCase gene [22]. Sage [21] described the leaf anatomy found in the *Portulaca* as being unique because of the apparent incompatibility of the photosynthetic pathways. The genus *Portulaca* shows nearly all members display C4 photosynthesis with attributes of the CAM pathway in the same leaf tissue and are considered facultative CAM species [18]. Previous research showed the CAM pathway aids in the retention of water for maintenance of the C4 pathway and the recycling of carbon to the mesophyll and bundle sheath cells [20]. This cooperation between the tissues may be the result of the close proximity of the tissues to each other because previous work has proposed that the tissues are functioning independently of each other [20].
