The uplift of the Andes reconfigured rivers in northern South America, one of the most species-rich regions on Earth. However, the impacts of these landscape changes on the evolution of aquatic plants had so far been overlooked. I will explore the role of Andean uplift and subsequent drainage basin formation on the evolution of riverweeds (Marathrum, Podostemaceae). Marathrum live attached to rocks in fast-flowing aquatic ecosystems from central America through northern South America. Phylogenomic, population structure, and divergence-dating analyses using target enrichment data show that the isolation of populations of Marathrum located in rivers across the Andes occurred in conjunction with major pulses of uplift. In addition, drainage basin reconfiguration resulted in secondary contact of previously isolated populations. Hybrids show the phenotype of one of the parental lines. Based on the results, I will present a proposal for timing and pattern of drainage basin formation across the Andes in northern South America and a novel perspective on the processes that shaped the evolution of the flora in the region.

I will discuss how the botanical collections made in this study and the historical records of Marathrum provide perspectives on the conservation of riverweeds and rivers.