Evolution of growth form in epiphytic Dissochaeteae (Melastomataceae)

We trace the evolution of root climbing and scrambling in Dissochaeteae and Sonerileae, two closely related groups that comprise the majority of Old World climbing Melastomataceae. The morphological and anatomical adaptations of the different climbers are interpreted in the context of a phylogeny based on chloroplast (cp) DNA sequences of the ndhF gene, generated for 31 representatives of Dissochaeteae and Sonerileae/Oxysporeae plus nine outgroups. For 20 of these taxa, the ndhF sequences were combined with cpDNA rp/16 intron sequences to obtain higher statistical support. Parsimony, minimum evolution, and maximum likelihood approaches yield congruent topologies that imply that scrambling growth evolved once in the common ancestor of Dissochaetinae, a group of similar to40 species centered around Dissochaeta and its close relatives Macrolenes and Diplectria. Root climbing, on the other hand, likely evolved in the common ancestor of Catanthera, Kendrickia, and Medinilla section Heteroblemma (together 26 species). In Melastomataceae overall, scrambling is restricted to Dissochaetinae, while root climbing has evolved several times. The scramblers are diverse in open disturbed habitats and show adaptations such as sarmentose branches, hook-shaped adventitious roots, and interpetiolar outgrowths that enhance their ability to lean on and clamber over other plants. Root climbers in the Catanthera-Kendrickia-Heteroblemma clade are restricted to humid habitats and show adaptations such as anomalous growth of the secondary xylem (a rare feature in the family), living climbing roots, and pseudoalternate phyllotaxy, which allows optimal arrangement of the normally opposite melastome leaves against the host's trunk.