2021/03/15 by Berkov-Kemp, Josiah, Hannum, Tyler, Ricks, Cassidy
#Cylindropuntia #adaptive plasticity #solar radiation #somatic mutation #spine density
paper · doi:10.21973/n37q2g
Intense solar radiation in desert ecosystems drives adaptation in cacti. Several Mojave Desert members of the cactus genus Cylindropuntia may exhibit morphological adaptations to reduce the impact of solar irradiation, such as light-blocking spines and the ability to point their new growth parallel to the sun’s rays. To detect adaptive morphologies in three Cylindropuntia species, we measured the orientation, spine density, and pigmentation of the new growth on the southwest and northeast sides of the plant. Additionally, we took morphometric measurements such as segment size to better understand how cacti allocate their resources and growth to cope with the sun. We found that two species of Cylindropuntia (C. echinocarpa and C. acanthocarpa) cacti do grow in line with the sun’s rays. We found no relationship between spine coverage and side of plant across all three species. For C. ramosissima, which bore the least number of spines on each of its segments, the results of damaging UV rays were frequently apparent in the form of stem-flattening somatic meristem mutations, despite their apparent investment in other pigment-based forms of defense. Two Cylindropuntia species display adaptive orientation but likely do not use spine density to avoid solar radiation. These results suggest that segment orientation is a more plastic trait than spine coverage in Cylindropuntia.