Insect Attracting Structures on Erodium Petals (Geraniaceae)

Abstract: Two types of structures previously unrecorded in Erodium petals are investigated. Spherical hairs filled with liquid resembling nectar droplets are exclusive to an ibero-mauritanic group of species included in Erodium subsect. Romana. Broad flat hairs which reflect light, shining as do nectar droplets, are restricted to most of the species included in Erodium sect. Malacoidea. Long, simple hairs in petals and sepals are involved in collection of nectar droplets. Some of them are arranged at the margin of the petal claw, just over the nectaries. Others are on the internal surface of sepals or on the upper surface of petals, serving apparently the same function. Their shape is aciculate or flattened. The nectar collected among the hairs forms shining spherical droplets, perceptible to insects. The glistening flat hairs and spheres shine in a similar way, probably mimicking nectar and attracting insects. Species with these special nectar-like structures produce nectar in quantities that can be observed by the naked eye, suggesting that these structures increase the attraction efficiency of flowers. Some taxonomic and biogeographic consequences are also discussed.