New evidence for bee-pollination systems in Aloe (Asphodelaceae: Aloideae), a predominantly bird-pollinated genus

Most Aloe species have long-tubed orange-red flowers, and many of these have been shown to be pollinated by birds. A few Aloe species have relatively short-tubed whitish or cream flowers, and one of these species, Aloe inconspicua, has been shown to be pollinated by insects. Here we further document exclusive insect-pollination in Aloe minima and A. linearifolia, two short-tubed summer flowering aloes in the grasslands of KwaZulu-Natal, South Africa. Despite sunbirds being present in the study area, only bee species were observed to visit and pollinate these two aloes. There was little difference in seed set between bird-excluded and open-pollinated treatments, indicating that bee visitors are effective as pollinators of these two species. In a few cases, a single visit by a bee was enough for successful fertilization. Other floral traits, including UV reflectance, small quantities of concentrated nectar, and the presence of floral scent (associated with pollination by insects), strengthen the argument for evolutionary specialization for exclusive insect-pollination in certain species of Aloe.