Morphology and evolution of the tarsal plantulae in Hymenoptera (Insecta), focussing on the basal lineages

The morphology of the plantulae (= tarsal pulvilli = plantar lobes), structures attached to the underside of the tarsus in Hymenoptera, was examined in 55 genera from all 14 families of the basal lineages of Hymenoptera ('Symphyta') and a few species of Apocrita, using scanning electron microscopy. Two distinct types of plantula were found: (1) integrated , an unsclerotized patch positioned ventro-distally on each tarsomere, and (2) distal , a membranous vesicle attached to the apical end of each tarsomere. The evolution of these two types is discussed in the light of current phylogenetic hypotheses. The plantulae exhibit an astonishing variety of form and structural details; their potential phylogenetic and taxonomic value is discussed.