AREOLE SPACING AND NUMBERS ON OPUNTIA LITTORALIS CLADODES ARE NOT ASSOCIATED WITH ENVIRONMENTAL CONDITIONS

Abstract

Opuntia species express great intraspecific morphological variability. All reproductive structures, cladodes (stem segments), and spines respond to macroenvironmental and microenvironmental variation and all of these form from areoles (axillary buds). However, little is known about areole response to light and temperature differences. In this study, I determined whether Opuntia areole numbers and spacing respond to environmental conditions. Terminal cladodes of Opuntia littoralis (Cactaceae) were sampled in Southern California. Data were collected for pad length, pad width, number of areoles on one pad face, number of areoles on the other pad face, and the distances to the nearest areole from the center one on one pad face and on the other for each pad for each of the four orientation groups (N-S, E-W, NW-SE, or NE-SW) for a total of 24 variables. Two-way analysis of variance, related-samples Wilcoxon signed rank tests, and Pearson product-moment correlation identified relationships across and between variables. Results show that areoles are a rather stable feature with regard to environmental variation; there were only small differences on cladode faces oriented in opposite directions. Areoles do not show the more dramatic responses to environmental variation typically seen on the structures borne from those areoles (such as cladodes and spines).