Surficial injuries of several long-lived columnar cacti of the Sonoran Desert, Mexico

Abstract

The giant cactus, Carnegiea gigantea (Engelm.) Britt. & Rose, of the Sonoran Desert of North America, is experiencing an epidermal browning of stem surfaces in which sheeting of epicuticular waxes leads to scaling and barking (epidermal browning). The purpose of this study was to determine the degree that four species of long-lived columnar cacti, namely, Stenocereus thurberi (Engelm.) Britt. & Rose, Lophocereus schottii (Engelm.) Britt. & Rose, Pachycereus pringlei (S. Wats.) Britt. & Rose and C. gigantea exhibit epidermal browning at a site in Sonora, Mexico where all four species occur. Estimates of scaling and barking of crests and troughs were made on stems and branches closest to 180° azimuth. All four species showed from 27 to 75% scaling and barking on crests. However, only C. gigantea exhibited scaling and barking on more than 40% of trough areas. The degree of scaling and barking of trough surfaces was correlated positively with degree of sheeting of epicuticular waxes, and negatively with number of visible stomata. These results show that symptoms of epidermal browning are not specific to C. gigantea but are present on all four cactus species observed.