Anatomical Characteristics of Sunlight-induced Bark (Periderm) Coverages on Columnar Cacti of Central Mexico

More than twenty-three species of tall, long-lived columnar cacti from a large variety of locations within the Americas show sunlight-induced periderm development on their stems. Periderm coverages lead to cactus morbidity and mortality. Our objective was to determine if periderm coverage patterns and anatomical characteristics of periderm formation differ among five cactus species located at a single site. Periderm coverages, patterns of periderm coverages and histological changes during the periderm formation process were determined for five native species of tall, long-lived columnar cacti in the Tehuacan Valley of Puebla, Mexico during May to June 2019. Periderm coverages and patterns of periderm on cactus surface varied among the species. On surfaces, some species had periderm form at crests initially, while one species had initial periderm form where troughs join. All species had the same internal tissues but the characteristics of these tissues varied among species. In response to periderm formation, one species retained its cuticle while one species retained its hypodermis intact and another produced cork cells inside the hypodermis. Overall, the histological changes that result from periderm formation were specific for each species and no pair of species showed the same responses to periderm formation. In conjunction with data from species from South America, eight distinct scenarios of histological manifestations were documented. Although, each of the five cactus species were in the same location and received the same amount of sunlight exposures, each species showed unique periderm coverages on surfaces, unique anatomical characteristics and unique anatomical responses. Thus, location was not the primary determinant of responses.