SURFICIAL INJURIES OF SEVERAL CACTI OF SOUTH-AMERICA

Analyses of several species of long-lived columnar cacti in Argentina and Chile show that an accumulation of epicuticular waxes is occurring on many species and that these accumulations obscure stomata. This accumulation leads to visible surficial maladies such as scaling and barking on crests and troughs of ribs similar to those that occur on saguaros, Carnegiea gigantea (giant saguaro) of North America, which results in premature death of individual saguaros. Scaling is the appearance of tan to red-orange discoloration of surfaces. Barking refers to a larger buildup of materials on the surfaces than scaling that appears dark brown to black. Equatorial facing surfaces showed more injuries on stems of Trichocereus pasacana and T. terscheckii in Argentina, and Echinopsis chilensis and E. scotsbergii in Chile, than on polar surfaces. Crest barking was as much as five times greater on equatorial-facing sides compared with polar-facing sides. Spine retention was up to three times greater on equatorial- vs polar-facing sides. The two troughs of a crest were evaluated separately. Results show that injury to one trough of a crest facing the equator was as much as twice that of the second trough being the south pole. These results show that surficial injuries were greater on equatorial than on polar surfaces, and are related to total incident irradiance on these surfaces.