Brigitte Fiala, Ulrich Maschwitz

• The paleotropical tree genus Macaranga (Euphorbiaceae) comprises all stages of interaction with ants, from facultative associations to obligate myrmecophytes. In SE.-Asia food availability does not seem to be the limiting factor for the development of a close relationship since all species provide food for ants in form of extrafloral nectar and/or food bodies. Only myrmecophytic Macaranga species offer nesting space for ants (domatia) inside intern odes which become hollow due to degeneration of the pith. Non-myrmecophytic species have a solidThe paleotropical tree genus Macaranga (Euphorbiaceae) comprises all stages of interaction with ants, from facultative associations to obligate myrmecophytes. In SE.-Asia food availability does not seem to be the limiting factor for the development of a close relationship since all species provide food for ants in form of extrafloral nectar and/or food bodies. Only myrmecophytic Macaranga species offer nesting space for ants (domatia) inside intern odes which become hollow due to degeneration of the pith. Non-myrmecophytic species have a solid stem with a compact and wet pith and many resin ducts. The stem interior of some transitional species remains solid, but the soft pith can be excavated. The role of different ant-attracting attributes for the development of obligate ant-plant interactions is discussed. In the genus Macaranga, the provision of nesting space seems to be the most important factor for the evolution of obligate myrmecophytism.…