Phylogenetic Patterns, Evolutionary Trends, and the Origin of Ant–Plant Associations in Piper section Macrostachys: Burger’s Hypotheses Revisited

In Flora Costaricensis, William Burger of the Field Museum in Chicago considered eight of the Piper species that occur in Costa Rica to make up the P. obliquum complex, and six additional species to be closely allied to it (Fig. 9.1; Burger 1971). Piper calcariformis, an additional species assignable to the P. obliquum complex, was later described by Tebbs (1989). Although Burger did not apply a system of infrageneric classification in Flora Costaricensis (1971), these 15 species of the P. obliquum complex and its allies represent all of the Costa Rican members of Piper sect. Macrostachys (Miq.) C.DC. Besides discussing the relationships between species, Burger (1972) also made hypotheses concerning evolutionary trends among the Costa Rican Piper species. In addition, he was among the first to note that certain Piper species have a tendency to support associations with ants. All known obligate ant-plants among New World Piper are found within the P. obliquum complex and its allies. In this chapter, we revisit Burger’s hypotheses regarding systematic relationships and evolutionary hypotheses, and explore the evolution of ant–plant associations more fully in the broader context of Piper sect. Macrostachys using a molecular phylogenetic approach. Molecular phylogenies are exceptionally useful as independent frameworks to study the evolution of ecological associations and the morphological traits related to them (Armbruster 1992, 1993, 1994, Dodd et al. 1999). Piper sect. Macrostachys, for many