Fruticose lichens often live in environments where airflow and atmospheric water input may influence their morphology. Measurements of the “pendulosity” (erect length/total length) of Usnea and Ramalina thalli growing on tall, cylindrical cacti in a fog-influenced desert show local-scale patterns that fit with aerodynamic theory. Windward thalli were shorter and more erect while leeward thalli were significantly more pendulous, consistent with expectations for the harvesting of water droplets from foggy air.